First you would find the area of the triangle which would be 84×92 then divide that answer by 2.
Then you will find the area of the circle using the given radius 20.5.
Lets work it out.
84×92=7728
7728÷2=3864 ft²
3864 ft² is the area of the backyard including the pool.
A=pi(20.5)²
A=1320.25 ft²
1320.25 ft² is the area of the pool.
Now we have to subtract to get the area of the backyard without the pool.
3864-1320.25=2543.75 ft²
2543.75 ft² is your answer.
Hope This Helps and God Bless!