\[\begin{array}{|c|c|c|} \hline 4 & 7 & 9 \\ \hline 8 & 6 & 8 \\ \hline 3 & 7 & 9 \\ \hline 35 & 49 & ? \\ \hline \end{array} \]
Rule by columns: Each bottom entry equals \[ (\text{top})\times(\text{middle})+(\text{bottom of the 3rd row}). \] Check first two columns: \[4\times 8 + 3 = 35\] , \(\quad\) \[7\times 6 + 7 = 49\] . So for the third column: \[ 9\times 8 + 9 = 72 + 9 = 81. \] \[ \boxed{81} \]
