Hi, I have a page that i have all the values displaying for baseprice, quantity, colour. but i don't know how to calculate the total price. attached is the relevant code i have but obv my totalprice calculation is wrong. any help much appreciated. thanks.

PHP Code:
<table cellpadding="6" cellspacing="0">
<tr>
<td width="160">Base Price:</td>
<td name="price" id="baseprice"><?php echo $row_products['product_price']; ?></td>
</tr>
<tr>
<td width="160">Size Variation:</td>
<td name="sizeprice" id="sizeprice"></td>
</tr>
<tr><td>
<select name="size" class="small" id ="size" onChange="changePrice()">
<option value="25.00">12 size</option>
<option value="30.00">14 size(+30.00 per unit)</option>
<option value="40.00">18 size(+40.00 per unit)</option>
<option value="45.00">20 size(+45.00 per unit)</option>
<option value="80.00">28 size(+80.00 per unit)</option>
</select>
</td><td></td></tr>
<tr>
<td width="160">Colour Variation:</td>
<td name="colourprice" id="colourprice"></td>
</tr>
<tr><td>
<select name="colour" class="small" id ="colour" onChange="changeColour()">
  <option value="">Please Select...</option>
  <?php
do {  
?><option value="<?php echo $row_colours['variation_price']?>"><?php echo $row_colours['colour_name']?> (+<?php echo $row_colours['variation_price']?>)</option>
  <?php
} while ($row_colours mysql_fetch_assoc($colours));
  
$rows mysql_num_rows($colours);
  if(
$rows 0) {
      
mysql_data_seek($colours0);
      
$row_colours mysql_fetch_assoc($colours);
  }
?>
</select>
</td><td></td></tr>

<tr>
<td width="160">Qty:</td>
<td name="qtyprice" id="qtyprice"></td>
</tr>
<tr><td>
<select name="qty" class="small" id ="qty" onChange="changeQty()">
  <option value="">Please Select...</option>
  <?php
do {  
?>
  <option value="<?php echo $row_quantity['product_price']?>"><?php echo $row_quantity['product_qty']?></option>
  <?php
} while ($row_quantity mysql_fetch_assoc($quantity));
  
$rows mysql_num_rows($quantity);
  if(
$rows 0) {
      
mysql_data_seek($quantity0);
      
$row_quantity mysql_fetch_assoc($quantity);
  }
?>
</select>
</td><td></td></tr>
<tr>
<td width="160" height="50"><div align="center"><strong>Total Price:</strong></div></td>
<td name="totalprice" id="totalprice"><div align="center">
<?php 
$totalprice
=$row_products['product_price'] + $sizeprice $colourprice $qtyprice
?>

<?php echo $totalprice?>

</div></td>
</tr>


</table>
<script>
    function changePrice() {
        document.getElementById('sizeprice').innerHTML=document.getElementById('size').value;
    }

    function changeColour() {
        document.getElementById('colourprice').innerHTML=document.getElementById('colour').value;
    }
    
    function changeQty() {
        document.getElementById('qtyprice').innerHTML=document.getElementById('qty').value;
    }
</script>