Agolf ball is given an initial speed of 20. meters
per second and returns to level ground. which
launch angle above level ground results in the
ball traveling the greatest horizontal distance?
[neglect friction.]
(1) 60.° (3) 30.°
(2) 45° (4) 15°

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.

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).