matrix $M=\left[\begin{array}{ccc}3& -5& 4\\ 5& 6& 1\\ 3& -4& -7\end{array}\right],$ and let $/$ be the $33$ identity matrix. If $N=7M+$I, then find $n_{31}.$

$21$

$28$

$35$

$29$

$22$