A Piece of Tin, Y = 17 Inches on a Side

Multiple Choice

A piece of tin, y = 17 inches on a side, is to have four equal squares cut from its corners, as in the illustration.If the edges are then to be folded up to make a box with a floor area of 81 square inches,
Find the depth of the box.

A) 4 in
B) 8 in
C) 11 in
D) 7 in
E) 9 in