if else statement in crystal reports 2016

Hello All

I have a column as "Source" in that data is

REC,PAY,PAY,REC,REC,REC,PAY like this

now i wanted to divide the data for payments and receipts.i have to write 2 formulas

if source is "rec" then it should display sum of Receipts in report footer based on amount field.

if source is "pay" then it should display sum of Payments in report footer based on same amount field.

can anybody tell me how to write the formula please.

Thanks

Paturi