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Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
Let's assume that the trip fuel for a given flight is 125kg and no limitations are imposed by runway lengths. Then the three checks for the take-off limit would be the least of:
Take off limit = 2950kg (structural limit)
Landing limit (2725kg) + burn-off = 2850kg
Max ZFW (2630kg) + all fuel on board = ???? this is what you are trying to find.
However, if ZFW was the problem, you could always go up to the next highest limit, 2850kg, providing the extra weight was fuel only. Adding extra fuel does not change the ZFW. In an exam question, the examiner would have to give you the empty aircraft weight, the pilot's weight, the passengers' weight and the cargo weight in the question text. So you would always know the actual ZFW (if that was greater than the maximum ZFW permitted, it's the examiner's fault for writing an invalid question!)
If a question asks for maximum fuel, there is no point checking the ZFW condition.