4.14 A credit union takes a sample of four mortgages each month to survey the homeowners' satisfaction with the credit union's servicing of their mortgage. Each mortgage is classified as a fixed rate (F) or variable rate (V). a. What are the 16 possible combinations of the four mortgages? Hint: One such possibility would be F1V2V3F4. b. List the combinations in event A: At least three of the mortgages are variable rate.