What is the approximate are of the the pool

area (pool)=area (rectangle)  -  area (triangle)

1) we calculate the area of the rectangle:
area (rectangle)=lenght x width
area (rectangle)=36 ft x 20 ft=720 ft².

2) we calculate the area of the triangle:
area (triangle)=(base x height) / 2
area (triangle)=(6 ft x 5 ft) / 2=15 ft².

3) we calculate the area of this pool:
area (pool)=720 ft²-15 ft²=705 ft²

the area of the pool is 705 ft².

What do you mean by that?