What is the distance between the zoo and the library?

max observes the zoo and the library from a helicopter flying at a height of
4003–√
feet above the ground

The answer is as follow

sin60° = 400√3 / H1, implies H1=  400√3 / sin60° 
sin30° = 400√3 / H2, implies H2=  400√3 / sin30° 
and the if the distance is D,
so we can find D such that D= H2 - H1=400√3 / sin30° - 400√3 / sin60°
D= 400√3(1/sin30°  - 1/ sin60°)=400√3(2-1.15)=338.11√3

The answer is "a"radius = 12.7 unitsdiameter = radius × 212.7 units × 2 = 25.4 units