Answer:
Distance between the library and the zoo = 600 units
Step-by-step explanation:
Given question is a problem based on 30°- 60°- 90° concept in height and distance.
In ΔABC
    ∠C = 60°
    Side AB = 300√3 units
     ⇒ Side BC = 300√3 ÷ √3 = 300 units (∵ In right triangle side
                       opposite to 60° angle is √3 times the other side)
Hence, BC =300 units
Now, in ΔABD
    ∠D = 30°
    BA = 300√3 units
     ⇒ Side BD = 300√3*√3 = 900 units (∵ In right triangle side
                     opposite to 30° angle is 1/√3 times the other side)
Now, CD = BD - BC = 900 - 300 = 600 units
Hence, distance between the library and the zoo = 600units