Oscar Olson, single, purchased a residence on February 19, 2017, for $170,000. On September 7, 2019, a tornado completely destroyed his home. The home was insured for its replacement value, and homes in Oscar's area had appreciated greatly. He received proceeds of $400,000.

a. How much does Oscar exclude and recognize?

b. If Oscar instead had received proceeds of $525,000, how much gain would be excluded and recognized? How much of a replacement residence would have to be purchased in order to exclude or defer all gain realized?