I agree with most of you say, but I think there are issues with the "Excess basis" in your calculation. The Excess basis can not be larger than the total basis (which is $200,000) for the replacement property. It can be calculated by two ways:
1. total cost of B + cost of selling A - sold price of A= 500,000 - 0 - 400,000=$100,000 ;
or
2. total cost basis of B - the adjusted basis for A= 200,000- (250,000-150,000) = $100,000;
