Lot 21 is a trapezoid with the two bases perpendicular to the road. The scale drawing below uses 1/2 inch = 40 ft.

A) 1/2 acre

B) 2 acres

C) 2 1/2 acres

D) 3 acres

So here's how I try to solve it:

A = 1/2 x 4 (5 + 3 1/2)

A = 1/2 x 20 x 8 1/2

A= 85

What am I doing wrong? What steps do I take?