a. The length/width for each rectangle is 10.5 because if you look at the bottom
It says 21 and 21/2=10.5 To find the width/length (aka the other side) I divided 10.5/3.5=3. Why 3.5? If you look at the bottom you will see the two rectangles at the bottom and then 3 and a half boxes on top of each rectangle. Then, all we have to do is simply multiply 10.5x3=31.5 - area
Answer - 31.5 square inches.
b. This is much simpler now. Since we know the length (aka the long line) is 10.5, we add that to 3 (aka the short line) and we get 13.5. Now all we have to do is multiply 13.5x21=283.5
Answer - 283.5 square inches.
Hope that helped you and good luck!