From the picture, the grass is only occupying the pink shaded area. Hence, we need to get the measurement of the pink shaded area only.
The formula for area of rectangle is A = L*W; where L= length and W = width
1.) Get the area of the whole landscape
A = 150 ft. * 100 ft.
= 15,000 sq. ft. is the area of the whole landscape diagram.
2.) Get the are of the other parts of the diagram
A = 20 ft. * 10 ft.
= 200 sq. ft. is the area of the white rectangle inside the diagram
A = 40 ft. * 30 ft.
= 1,200 sq. ft. is the area of the bigger grey-shaded rectangle
A = 20 ft. * 15 ft.
= 300 sq. ft. is the area of the smaller grey shaded rectangle
3.) Subtract the total measurement of the other parts from the measurement of the whole diagram
15,000 - (200+1,200+300) = 13,300 sq. ft.
4.) Therefore, A.) 13,300 sq. ft. is the area of grass in the home landscape diagram.