Hey everyone! I need some help again, on a calculator I'm trying to develop. Basically I've a selector in html and besides that an input where you can add a number. The selector contains some options and each one of the options has a value assigned to it. What I want to do is to get that value of the option and multiply it with the number of the input and get the result as an altert. This is what I've so far:

HTML Code:
<select name="Elements" id="a"> 
	<option value="0">(Selecciona un element)</option>
	<option value="1">Hidrogen</option> 
	<option value="2">Liti</option> 
	<option value="3">Berili</option> 
	<option value="4">Bor</option>
<input type="text" maxlength="2" id="b"> 
<input type="submit" value="Calculate" name="Caltulate" onclick="Multiply(document.getElementById('a').value,document.getElementById('b').value);">
	function mol (a,b) {
	var r = Number(a)*Number(b);
I know both codes aren't probably what I need, since I want to get the value of the selector not the id, so that needs to be fixed as well as the javascript code. Thanks for your help!