Need help with Physics word problem

A man is 2,000 m from the base of a tower and is launching a rocket in the direction of the same tower. When the rocket takes off the change in the angle between the flight path and the land is represented by Φ(t) according to time. Knowing that Φ'(t) = Π/3, determine: 

 1. The height of the rocket when Φ = Π/3 radians. 

Please explain how you arrived at your answer.