another 1

[sougatau]

in 1 table there are are 3 feilds
folwer_name
no_of_flowers
total_cost


another table (2 fields)
name
price

eg:
name price
rose 15
tulip 20


Now I want o make a form
with 3 fields

folwer_name
no_of_flowers
total_cost


eg: if some one select 'flower_name' 'rose' and quantitly '10' then total_cost = 150

How can I do this ? using query or anything else plz gimme detals