Transact SQL :: Picking Up Average Last Two Payments

Got a table named Payments in the following form:

Report_DateCustomer_IDCustomer_NamePayment_DatePayment_Amount

The Customers Table have the fields:

Customer_IDCustomer_Name

Since the Customers Table contains the complete list of customers I seek to have a Join made between it and the Paymentstable to check the amount made by the customers.

However, the trouble arises when I seek to check the average amounts made by each customer during last two months in which such a customer had paid.

In further clarification, lets consider current month of May 2015 going on;

Customer_A had paid $10,000 in AprilCustomer_A had paid $5,000 in AprilCustomer_B had paid $10,000 in AprilCustomer_A had paid $18,000 in MarchCustomer_A had paid $2,000 in MarchCustomer_A had paid $10,000 in FebruaryCustomer_B had paid $8,000 in FebruaryCustomer_B had paid $4,000 in FebruaryCustomer_B had paid $3,000 in February...