The area of the whole rectangle is 91cm. Subtract 2 because of what is not shaded in the bottom right, then subtract 12 from what is not shaded in the top left. That leaves you with 77cm of shaded area.
I believe the answer is 77 cm squared because when you multiply the white areas-2 and 12- then multiply 13 times 7 after that adding the two white areas together and subtracting that from 91-7 times 13- you get 77.
