Every time you go flying you will consider 3 limits....MTOM, MZFM, and MLM.
MTOM and MLM are either structural or performance limits (depending on conditions), MZFM is a structural limit. Its up to you to ensure you do not exceed these limits...for any set of conditions, one of these limits will offer the 'critical value' in terms of payload or fuel.
For this question you are only concerned with fuel, so MZFM doesn't come into it....
A table will help

T/O LAND

LIMIT 4200 3700
DOM 2800 2800
LOAD 400 400
FUEL 1000 500
So max fuel at T/O is 1000kgs and max fuel at landing is 500kgs; now add the trip fuel to the landing fuel....300+500=800kgs
Therefore, max fuel at T/O dictated by the MLM limit....you can T/O with 800kgs of fuel (within MTOM limit), you will then land at MLM.