Radio buttons and mathematics

I am using version 1.3.9h and current theme 'Avignon'.

I have setup a radio button with 4 selection options; 10; 20; 50 & 100.

Each select option I have added, using Attributes Controller, the price attribute.

What I would like to do is;

using the radio button selection, lets say 20, I would like to use this figure and multiply that be qty required and then deduct that from the qty available.

For example I what 20 pack and I want qty of 3 that equals 60. Now the qty available is 150 so after the above has been done the resultant available will then be 90.

Here you are http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=310

~Melanie

You Star. Thanks for that. There is so much on this forum, I find it difficult to find what I require.

Thank you:clap::bigups:

I must have does something wrong. The install has not worked.

Installed the SQL then the install of includes etc. However I have noticed that in the instructions it does say to change two YOUR-TEMPLATES I only had one to change. The one missing was in modules.

Any ideas?

I have installed the plugin mentioned and I do not have the qty decrease, in fact nothing happens. It stays at the qty I have set.:oops: