The question asks the landing mass at the alternate.
It gives all the elements of the fuel load.
The answer marked as correct assumes you arrive at your alternate with both reserve fuel and contingency on board but we think this is wrong.
We would assume you had used any 'spare' fuel such as unburnt contingency shooting approaches before you made the decision to divert and you would therefore arrive with only reserve fuel on board.
There is no answer that matches this reasoning, but the closest answer is the one marked as correct.