now, originally, you have L for length and L-2 for width..
but since the 2x2 was cut on the corners, the new length would be L-4 and the new width would be (L-2)-4=L-6.
a box is 70 cubic units = 2(L-4)(L-6) = 2(L^2 - 10L + 24)
so, L^2 -10L + 24 - 35 = L^2 -10L - 11 = 0
factoring, you would get (L - 11)(L + 1) = 0 --> L=11 or L= -1.
since there is no negative distance, answer is L=11.
so the width is 9.