A Carnot engine ($CE_1$) works between two temperature reservoirs $A$ and $B$, where $T_A$ = $900$ $K$ and $T_B$ = $500$ $K$. A second Carnot engine ($CE_2$) works between temperature reservoirs $B$ and $C$, where $T_C$ = $300$ $K$. In each cycle of $CE_1$ and $CE_2$, all the heat rejected by $CE_1$ to reservoir $B$ is used by $CE_2$. For one cycle of operation, if the net $Q$ absorbed by $CE_1$ from reservoir $A$ is $150$ $MJ$, the net heat rejected to reservoir $C$ by $CE_2$ (in $MJ$) is ______________