The question usually says 25% reserve of REMAINING trip fuel, which means the actual amount of reserve fuel required is decreasing as the flight progresses and would be zero on arrival.
RichardH, I don`t absolutely agree with you. Trip fuel is fuel for all the trip, which is 3:30. If the final reserve should be 25% Trip, it is related to the Total Trip fuel, not just remaining time, as you say.
Your theory would say, that after landing, you can have zero final reserve, which you surely know is not true.
So after my calculations, the result is also 136.
Please, anyone correct me if I`m wrong.