The ZFM and TOM limits
shown in the diagram are in fact incorrect, they
should be MZFM 51300kg and MTOM 62800kg, the structural limit.
So the examiner has got
this bit wrong.
However regardless of
this error, the answer still comes from column (c). 54245 =
7355= 61600kg.
Subtract from this the
Operating mass (DOM +take-off fuel) 35720+13700 =49450kg. 61600-49450 = 12150kg
Subtract from this the
current traffic load to find the underload: 12150-10320=1830kgs.