The answer is 19,428, but I could only get there by Googling 'MRJT' to get the missing information:
DOM + all of the fuel is 43,372.
MTOM (MSTOM) is 62,800 for the MRJT, that leaves you with 19,428 for payload (allowable traffic load).
$$62,800 - (27,372 + 12,000 + 4,000) = 19,428$$
Below you can see the calculations for MTOM, MLM, and MZFM. Since the traffic load for the 'MTOM limited case' is the lowest, the maximum 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}$
(Table courtesy of DeltaLima)