hie.. i need help from expert here.. solution required
for info, i'm try to develop it for my own website which contain price calculator, to be link to shopping cart and paypal

1) i am stuck on the quantity which supposed to be 'times the subtotal price'
><span style="font-size: 12pt;"><strong>canvas print</strong></span></p>

<form name="myform">

<select NAME="canvasItem" onchange="calculatePrice()" id="canvasItem">
<option value="0">- select type of canvas -</option>
<option value="8">Polyester 280 gsm</option>
<option value="9">Cotton 320 gsm</option>
</select><br />

<select name="sizeItem" onchange="calculatePrice()" id="sizeItem">
<option value="0">- select size -</option>
<option value="1">300mm x 300mm [+- 12"x12"]</option>
<option value="1.5">300mm x 450mm [+- 12"x18"]</option>
<option value="2">300mm x 600mm [+- 12"x24"]</option>
<option value="2.25">450mm x 450mm [+- 18"x18"]</option>
<option value="3">450mm x 600mm [+- 18"x24"]</option>
<option value="3.75">450mm x 750mm [+- 18"x30"]</option>
<option value="4">600mm x 600mm [+- 24"x24"]</option>
<option value="5">600mm x 750mm [+- 24"x30"]</option>
<option value="6">600mm x 900mm [+- 24"x36"]</option>
</select><br />

<select name="colorItem" onchange="calculatePrice()" id="colorItem">
<option value="0">- select color -</option>
<option value="1">Black and White</option>
<option value="1.1">Color</option>
</select><br />

<select name="qualityItem" onchange="calculatePrice()" id="qualityItem">

<option value="0">- select quality mode -</option>
<option value="1">Economy</option>
<option value="1.333">High</option>
Numeric restrictions will apply in the input field:Quantity :</select>
<p>Quantity :&nbsp;<input max="100" min="1" name="quantity" type="number" /></p>
<p><button type="button">Calculate</button> New Calculated Price, RM:<input id="PicExtPrice" size="8" type="text" /></p>

function calculatePrice(myform){

//Get selected data
var elt = document.getElementById("canvasItem");
var canvas = elt.options[elt.selectedIndex].value;

var elt = document.getElementById("sizeItem");
var size = elt.options[elt.selectedIndex].value;

var elt = document.getElementById("colorItem");
var color = elt.options[elt.selectedIndex].value;

var elt = document.getElementById("qualityItem");
var quality = elt.options[elt.selectedIndex].value;

//convert data to integers
canvas = parseInt(canvas);
size = parseInt(size);
color = parseInt(color);
quality = parseInt(quality);

//calculate total value
var total = canvas+(size*color*quality);

//print value to PicExtPrice


2) the shown subtotal have no decimal, which i required 2 decimal as its for the PRICE
3) how to export the calculated price to shopping cart and shopping cart ke paypal?