So first you should find the area of the rectangle on the bottom.
18x12=216
Then find the area of the trapezoid. I believe the formula is A = a+b/2(h).
So do 10 + 18 = 28, divide by 2, which is 14, then multiply by the height, 6, and you get 84.
Now you add the area of both shapes together, 216+84=300.
300 ft is your answer.
If you have questions lmk