Table based calculation on repeating rows with input fields

I’ve hacked together a calculator, it features one row to begin with that accepts user inputs to specify height (from dropdown), width, depth, qty (text fields).

It then performs a calculation (width+depth) * multiplier +12
The multiplier is defined by an IF based on the selected height.

I want to add 10 or more rows which are identical, and then get a grand total for all the rows’ totals added together.

Where I am stuck is how to change the drawerPrice function to handle extra rows.

I basically know nothing about js, this is a result of day 1.

<script type = "text/javascript">
      //<![CDATA[
      
	  function orderTotal(){
        var txtOutput3 = document.getElementById("txtOutput3");
	  	var finalTotal = 0;
		finalTotal = parseFloat(finalTotal) + parseFloat(drawerSub);
		
		finalTotalVat = (finalTotal * 0.175) + finalTotal;
//round to two decimals
		finalTotalVat = Math.round(finalTotalVat*100)/100;


		txtOutput3.innerHTML = finalTotal + "<br/>+VAT: " + finalTotalVat;

	  }       
		
 
      function drawerPrice(){
														
				var boxHeight = document.getElementById("boxHeight");
				var boxWidth = document.getElementById("boxWidth");
				var boxDepth = document.getElementById("boxDepth");
				var boxQty = document.getElementById("boxQty");
				var txtOutput = document.getElementById("txtOutput");
				var txtOutput2 = document.getElementById("txtOutput2");
					
				// get user inputted values for dimensions
				var height = boxHeight.value;
				var width = boxWidth.value;
				var depth = boxDepth.value;
				var qty = boxQty.value;
					
				// calculate multiplier
				var multiplier = 0;
				if (height == 77) {
					multiplier = 0.018;
				}
				else 
					if (height == 102) {
						multiplier = 0.018;
					}
					else 
						if (height == 127) {
							multiplier = 0.022;
						}
						else 
							if (height == 152) {
								multiplier = 0.026;
							}
							else 
								if (height == 177) {
									multiplier = 0.038;
									}
								else 
									if (height == 202) {
										multiplier = 0.045;
									}
				
				// unit drawer cost
				var drawerCost = (parseFloat(width) + parseFloat(depth)) * parseFloat(multiplier) + 12;
				//round to two decimals
				drawerCost = Math.round(drawerCost * 100) / 100;
				// multiply for quantity
				drawerSub = drawerCost * parseFloat(qty);
				
				// Lastly convert to currency format (fixed 2 decimal places length) - gives results as STRING
				drawerCost = drawerCost.toFixed(2);
				drawerSub = drawerSub.toFixed(2);
				
				// output values
				txtOutput.innerHTML = drawerCost;
				txtOutput2.innerHTML = drawerSub;
				
				}


      //]]>
    </script>

The HTML is:

<form action = "">
<fieldset style="background-color:#cccccc; width:475px; border:0; margin:0;">
<table width="100%" border="0">
	<tr>
		<td align="center"><b>Height</b></td>
		<td align="center"><b>Width</b></td>
		<td align="center"><b>Depth</b></td>
		<td align="center"><b>Qty</b></td>
		<td align="center"><b>Calc</b></td>
		<td align="center"><b>Cost</b></td>
		<td align="center"><b>Subtotal</b></td>
	</tr>
	<tr>
		<td align="center">
			<select id = "boxHeight">
<option value = "77">77mm</option>
<option value = "102">102mm</option>
<option value = "127">127mm</option>
<option value = "152">152mm</option>
<option value = "177">177mm</option>
<option value = "202">202mm</option>



</select>
</td>
		<td align="center"><input type = "text" id = "boxWidth" size="5" /></td>
		<td align="center"><input type = "text" id = "boxDepth" size="5" /></td>
		<td align="center"><input type = "text" id = "boxQty" size="2" /></td>
		<td align="center"><input type = "button" value = "Cost" onclick = "drawerPrice()"/></td>
		<td align="right"><span id = "txtOutput"></span></td>
		<td align="right"><span id = "txtOutput2"></span></td>
	</tr>
	
	<tr>
		<td colspan="7" align="right"><hr/><input type = "button" value = "Total" onclick = "orderTotal()"/><br/>
		<span id = "txtOutput3"></span></td>
		
		
	</tr>

</table>	

</fieldset>
</form>

If there is no clever way to do it, I guess I will just create a function for each row that does the same thing so each cost button calls a different numbered row function eg drawerCost1, drawerCost2…