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.