Question 30
A $9 \times 9$ square is divided into $81$ small $1 \times 1$ squares, $8$ of which are painted black, the rest being white. We cut a fully white rectangle (possibly, a square) out of the big $9 \times 9$ square. What is the maximal area of the rectangle that we can attain regardless of the positions of the black squares? It is only allowed to cut the rectangle along the grid lines.