Help with Combinations

[rhath127]

Hey guys, 

I am working on a way a customer can order balloons to be picked up in store. 

I am having some difficulty getting it right.

Step 1: Choose balloon

Step 2: Choose balloon quantity

Step 3: Choose how many weights (if any) are required.

-- this is where it stops working -- 

I need the page to independently calculate how many balloons ($1.50 x 10) and add on the cost of weights ($2.50 x 2, for example). Total should be $20 but what its doing now is adding the cost of weight $2.50 to balloon $1.50 and making it $4 x 10. Which isnt right. 

http://balloons.partyandyou.com.au/home/96-copy-of-navy-blue-28cm.html

 

any help would be greatly appreciated