They are about the same length. 8 mm is 0.314961 inches. 5/16 inches in decimal form is 0.3125 inches.
The area of a triangle is calculated by multiplying the base and the height, then dividing that value by 2.
(1/2)bh
You find the area of trapezium: 45
Then lower shape, triangle: 13.5
Then you add both:
B) 58.5 square feet:))
= 81
