Answer:
(4) 90.°
Step-by-step explanation:
The maximum height reached by the ball depends on the vertical velocity of the ball: the greater the vertical velocity of the ball, the higher the ball will go.
The vertical component of the velocity of the ball is given by:

where
 is the initial speed of the ball
 is the initial speed of the ball
 is the angle at which the ball is thrown
 is the angle at which the ball is thrown
Therefore, 
 will be maximum when
 will be maximum when 
 . And by solving this equation, we find that the angle that satisfies this condition is
. And by solving this equation, we find that the angle that satisfies this condition is 
 , which corresponds to throwing the ball straight up.
, which corresponds to throwing the ball straight up.