So we have to let the user input the weight of an item between 0 and 400. and depending on the weight the price per pound is different.

0 - 150 lbs = $20
151 - 300 lbs = $15
301 - 400 = $10

On top of this, there are 3 radio buttons, 50% discount, 25% discount, and No Discount. I'm having trouble detecting which radio button the user has selecting and obtaining the value that i have put for it in the HTML. If somebody could guide me in the right direction, it would be greatly appreciated. Here is my JavaScript...

Code:
<script type="text/javascript">	

function shippingTotal() {
	
	var itemweight = parseInt( document.getElementById("itemweight").value );
	var disc50 = document.getElementById("disc50").value;
	var disc25 = document.getElementById("disc25").value;
	var disc00 = document.getElementById("disc00").value;
	var subtotal;
	var weighttotal;
	var discount;
	var grandtotal;
	
	if ( itemweight < 0 || itemweight > 400 ) {
	
		msg = "<div id='alertmsg'>That weight is not accepted. Please try again.</div>";
	
	} // <- ends if below zero or over four hundred
	
	else { // <- first radio button
	
		if  ( disc50.checked = true ) {
	
			if ( itemweight > 0 && itemweight <= 150 ) {
				
				weighttotal = itemweight * 20;
				subtotal = itemweight * disc50 * 20;
				discount = ( disc50 / 100 ) * 20;
				grandtotal = weighttotal - discount;
				
				msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
				msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Discount rate is " + disc50 + "%</div>";
				msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
				
			} // <- ends itemweight is between zero and one fifty
			
			else {
				
				if ( itemweight > 150 && itemweight <= 300 ) {
					
					weighttotal = itemweight * 15;
					subtotal = itemweight * disc50 * 15;
					discount = ( disc50 / 100 ) * 15;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc50 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
					
				} // <- ends itemweight is between one fifty and three hundred
				
				else {
					
					weighttotal = itemweight * 10;
					subtotal = itemweight * disc50 * 10;
					discount = ( disc50 / 100 ) * 10;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc50 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
			
				} // <- ends itemweight between three hundred and four hundred
		
			} // <- ends else about not being between zero and one fifty
			
		} // <- ends else  between zero and four hundred
	
		else { // <- second radio button
		
			if  ( disc25.checked = true ) {
	
			if ( itemweight > 0 && itemweight <= 150 ) {
				
				weighttotal = itemweight * 20;
				subtotal = itemweight * disc25 * 20;
				discount = ( disc25 / 100 ) * 20;
				grandtotal = weighttotal - discount;
				
				msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
				msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Discount rate is " + disc25 + "%</div>";
				msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
				
			} // <- ends itemweight is between zero and one fifty
			
			else {
				
				if ( itemweight > 150 && itemweight <= 300 ) {
					
					weighttotal = itemweight * 15;
					subtotal = itemweight * disc25 * 15;
					discount = ( disc25 / 100 ) * 15;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc25 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
					
				} // <- ends itemweight is between one fifty and three hundred
				
				else {
					
					weighttotal = itemweight * 10;
					subtotal = itemweight * disc25 * 10;
					discount = ( disc25 / 100 ) * 10;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc25 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
			
				} // <- ends itemweight between three hundred and four hundred
		
			} // <- ends else about not being between zero and one fifty
			
		} // <- ends else  between zero and four hundred
			
		} // <- ends second radio button else
		
		else { // <- third radio button
		
			if  ( disc00.checked = true ) {
	
			if ( itemweight > 0 && itemweight <= 150 ) {
				
				weighttotal = itemweight * 20;
				subtotal = itemweight * 20;
				discount = 0;
				grandtotal = weighttotal - discount;
				
				msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
				msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Discount rate is " + disc00 + "%</div>";
				msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
				msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
				
			} // <- ends itemweight is between zero and one fifty
			
			else {
				
				if ( itemweight > 150 && itemweight <= 300 ) {
					
					weighttotal = itemweight * 15;
					subtotal = itemweight * 15;
					discount = 0;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc00 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
					
				} // <- ends itemweight is between one fifty and three hundred
				
				else {
					
					weighttotal = itemweight * 10;
					subtotal = itemweight * 10;
					discount = 0;
					grandtotal = weighttotal - discount;
					
					msg = "<div id='resmessage'>Total weight is " + itemweight + " pounds</div>";
					msg = msg + "<div id='resmessage'>Weight cost is $" + weighttotal.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Discount rate is " + disc00 + "%</div>";
					msg = msg + "<div id='resmessage'>Discount amount is $" + discount.toFixed(2);  + "</div>";
					msg = msg + "<div id='resmessage'>Total cost is $" + grandtotal.toFixed(2);  + "</div>";
			
				} // <- ends itemweight between three hundred and four hundred
		
			} // <- ends else about not being between zero and one fifty
			
		} // <- ends else  between zero and four hundred
			
		} // <- ends third radio button else
			
	}// <- ends else about the itemweight being between zero and four hundrred
	
	document.getElementById("results").innerHTML = msg;
		
} // <-ends function shippingTotal
</script>