Question

A golf ball is given an initial speed of 20. meters

Answer 1

In calculus, neglecting air resistance, the formula for range is R = v(0)^2 sin 2A/g, where v(0) is the initial speed, A is the angle, and g is the acceleration of gravity. Here v(0) = 20 m/s, and g is a constant. 

R = 400 sin 2A 

For maximum range, sin 2A = 1, so 2A= 90°, and A=     45 

45 degrees  is my answer.

Answer 2

Neglecting air resistance, the greatest horizontal distance
always results from a launch angle of 45° above the horizon,
no matter what the initial speed is.  This is a handy thing to know. 
You'll use it many times, and you should carry it in your toolbox
(i.e. memorize it).