Select item then quantity in custom fields

Hi Tuan

I need to add a field in a form where the customer selects an item which then brings up a box to add amount in that generates a fee per item. Is this possible?
For example we are offering 3 lunch packs, Vegetarian, Dairy Free, Gluten Free. Customer selects Vegetarian and then can put in how many, say 2 at $20 each which then sets the total for $40 added to the event cost. 
The only way I see is to do a list with the option set multiple times ie 1 Box, 2 Box, 3 Box.

Hope you can help!

Thanks

Christina

This should work.
joomdonation.com/forum/events-booking-ge...lds-calculation.html

Thanks Sunil,

I'll give that a go.

OK Christina. Please continue setting it up and let us know if you need assist

Thanks Sunil for helping us with answering the questions

Tuan

Thanks Tuan

It works to a degree however it adds $20 to the price before even making a selection, then when I put an amount in the textbox it is $20 too much. I'm not sure what I have done wrong.