Queries :: Applying Calculations To Date Ranges

I need a query that will relate values to given date ranges. For Example:

Table: TaxTypeRange
Values:
TaxType; FromDate; ToDate; Contact
W2; 1/1/15; 3/31/15; Tom
1099; 4/1/15; 6/30/15; Tom
W2; 7/1/15; 12/31/15; Tom

Table: Bills
Values:
Contact; BillAmount; BillDate
Tom; 1000; 3/31/15
Tom; 1100; 4/30/15
Tom; 1200; 5/31/15
Tom; 1300; 6/30/15
Tom; 1400; 7/31/15

Requirement: For every period where the TaxType = W2 the query should multiply the Bill amount by 1.20, so the result should be something like this:

Query: BillsAndTax
Values:
Contact; BillAmount; BillDate; TotalBill
Tom; 1000; 3/31/15; 1200 (TaxType = W2 so 1000* 1.2)
Tom; 1100; 4/30/15; 1100 (TaxType = 1099 does not apply 1.20)
Tom; 1200; 5/31/15; 1200 (TaxType = 1099 does not apply 1.20)
Tom; 1300; 6/30/15; 1300 (TaxType = 1099 does not apply 1.20)
Tom; 1400; 7/31/15; 1680 (TaxType = W2 so 1400 * 1.2)

Not sure how to set this up the right way.