Paypal html shipping,shipping2 code

[ty1150]

In regards to shipping costs I have experimented with "shipping,shipping2". I need help with a variable that will allow my buy now buttons to handle a shipping structure as follows:

1 item shipping cost $6.95
2 items shipping cost $7.95
3 items shipping cost $8.95
4 items up to 20 items shipping cost $9.95
20 items up to 40 items shipping cost $10.95 etc.

Shipping, shipping2 works fine for 1 to 4 items. I need 5 through 20 items to remaine $9.95

I am a bit confused as to set up java script to handle this function. I need to ask someone to "hold my hand" through the process.

Currently I have:

<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="image" src="https://www.paypal.com/en_US/i/btn/x-click-but22.gif" border="0" name="submit" alt="Make payments with PayPal - it's fast, free and secure!">
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
<input type="hidden" name="add" value="1">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="business" value="customersupport@unbelievableprices.biz">
<input type="hidden" name="item_name" value="absolu 1.7 oz Eau De parfum Spray">
<input type="hidden" name="amount" value="40.00">
<input type="hidden" name="no_shipping" value="2">
<input type="hidden" name="return" value="http://www.unbelievableprices.biz">
<input type="hidden" name="cancel_return" value="http://www.unbelievableprices.biz">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="bn" value="PP-ShopCartBF">
</form>

Please advise,