One service, different prices for it/city

[atisz]

Another problem, I think same simple solution, as for the previous one.

One form with 2 subforms.
Fields on Form:
ID
First name
Last name
City
..............

Fields on Subform1:
Month
Quantity (calculated on form)
Price2Pay (calculated on form)
............

Fields on Subform2:
Month
Price
.........

The 2 subforms are connected by Month, Price2Pay=Quantity*Price.
Everithing is simple if the price is the same for all cities. But the problem is that it isn't.
How can I calculate the Price2Pay, in this case?

Thanx!

 

[atisz]

??????????????????

Nobody can't help me?
I know I have to put some other fields in my price table, and then manage somehow this:
if city=city1 and month=month1 use price1
if city=city2 and month=month1 use price2
..........................................................

or something like that.
Help please!!!!!!!!!!