Answer:225
Explanation:
we start by finding the area of the unshaded triangles and subtracting them from the total area of the box.
The total length of the top is 20 and the total length of the bottom side is 18
20-18=2 so the small unshaded part on the bottom side is 2. with this we can find the left triangle. triangle area is base times height over 2 so the area of the unshaded triangle on the left is 15*2/2=15.
We know the small unshaded bit on the right side is 6 as it is shown on the diagram. again, we can use base times height over 2 to get the area of the top unshaded triangle. 6*20/2= 60.
We can do base times height to find the total area of the rectangle
15*20=300
300-15-60=225