Use the formula for the area of a trapezoid, which is 1/2(b1+b2)h, where b1 and b2 are your bases.
1/2(10+18)*6
=1/2(28)*6
=14*6
=84
Then you proceed to find the area of the rectangle, which is l*w.
12*18=216
Add up the areas to get a total area of 300 ft^2
:)