Draw it and it will make things easy for u .

Basically they’re asking if you removed the 4th row and 7th column then how many squares will you remain with on the board.

Hint: total number of squares on board = rows x columns = r(rows) x r+1(columns) = r^2+r

and you’ve been given that r>10

also when asking PowerPrep question add a spoiler to the heading!