Answer is 19,428.
DOM + all of the fuel is 43,372.
MTOW (MSTOM) is 62,800 for the MRJT, that leaves you with 19,428 for payload (allowable traffic load).
$$62,800 - (27,372 + 12,000 + 4,000)$$
Somewhere in the textbook the MTOW should be listed, the question as is now is unsolvable.
Below you can see the calculations for MTOM, MLM and MZFM. Since the traffic load for the MTOM limited case is the lowest, the traffic load for the flight is 19 428 kg.
$ \begin{array}{|l|c|c|c|c|cc|} \hline & &\textrm{DOM} & \textrm{trip fuel} & \textrm{landing fuel} & &\textrm{traffic load} \\\hline MTOM: & 62800 & -27 372 & -12000 & -4000 & = & 19428 &\leftarrow\textrm{limiting} \\\hline MLM: & 54900 & -27372 & & -4000 &=&23528\\\hline MZFM: & 51300 & -27372 & & & = &23928 \\\hline \end{array}$
I got the 62,800 figure by Googling 'MRJT'.
