The formula for the area of a trapezoid is 1/2 (b1 + b2) h
So, take your b1 and b2, 12 and 6, and add them together. You get 18.
Divide this by 2, and you get 9.
Now, multiply 9 by your height, which is 4.
9 x 4 = 36.
The area of the trapezoid is 36 square inches.