From a point p on level ground, the angle of elevation of the top of a tree is 60°. if the tree is 39m high, how far is its base from p

Start by drawing a picture of the problem, to gain a better understanding of what you're dealing with, 

In this case we will be using the function, cosine which is adjacent / hypotenuse

Cos(60) = x / 39 

Simplify, 

x = 39cos(60) which brings us to the solution of 19.5 meters. 

Answer is negative 2