You can cut the polygon into 2 rectangles. Subtracting 18 from 60 can give you the length of rectangle A, so 42 will be the new length for rectangle A.
Multiply 6 and 42 to get 252 for the area of rectangle A.
Multiply 18 and 30 to get 540 for the area of rectangle B.
(You multiply to find the area.)
Lastly you add both areas, 252 + 540, and the final result is:
