You have a 4 x 8 piece of red paper. You will place a 3 x 7 piece of blue paper on top which covers part of the red paper.
Since the 3 x 7 paper does not completely cover the red paper, some of the red paper on the bottom will still be visible when viewed from above. The question is then, how much of the red paper is still visible?
The answer is simply an area question.
You have 32 square cm of red paper and 21 square cm of blue paper covers the red paper. Therefore, 32-21 = 11 square cm of red paper is still visible.
