can you explain step by step how NPV was calculated?

Fitzgerald, Incorporated, currently has an all-cash credit policy. It is considering making a change in the credit policy by going to terms of net 30 days. The required return is .61 percent per month. Calculate the NPV of the decision to change credit policies. (A negative answer should be indicated by a minus sign. Do not round intermediate calculations and round your answer to 2 decimal places, e.g., 32.16.)