72 in².
Explanation:
First find the area of the entire rectangle. Do 8 inches×10 inches to get 80 inches².
Then find the area of the triangle with the dotted lines. We know that the base is 4 inches since we are given that the solid line next to the base is 4, so if we subtract that from the bottom 8 inches we get 4.
Then the height we know is also 4 inches because if we subtract 6 inches from the short side from 10 inches on the long side.
Using the a=bh½ formula, you can do 4×4 which is 16 divided by 2 to get 8 inches². Do the area of the rectangle minus the area of the triangle, so 80-8, and then you get 72 inches².
Hope this helps :)
