The problem is modelled in the diagram below
Question 1:
The largest area of the pool is half of the area of the circle
Area of circle = πr², where r is the radius given by 1/2 of the diameter
Area of circle = π(60)² = 11309.73355 feet
Area of half of the circle is 11309.73355/2 = 5654.866... ≈ 5654.87 feet (2dp)
Question b:
The area of the pool is the area of the circle subtracts the area of the triangle.
The area of the circle is 11309.73²
The area of the triangle is 1/2 (60×103.92) = 3117.6 feet²
The area of the pool is 11309.73 - 3117.6 = 7922.13 feet²
The volume of the pool = 7922.13 × 4 = 31688.52 feet³
Note: there isn't any information on the fish tank part so the answer above is assumed for the whole pool.