Only vertical component of the velocity is relevant to this problem.

The equation describing the height of the ball above the ground in this problem is

 = ,  or  (which is the same)

 = .     (1)

Here t is the time the volleyball is in the air, and  in the right side is the ground level.

Solve this quadratic equation for t, and choose an appropriate root.


Now a bit more explanation.
If the object is thrown vertically with the initial vertical velocity "v" from the initial height , its height h(t) is a quadratic function

h(t) = .    (2)

It will hit the ground when h(t) = 0.

Here "g" is the gravity acceleration, also known as "free fall acceleration"

The value for g is about 9.81  near the Earth surface.

Based on this info, the equations (1) and (2) above are written.

Now solve the quadratic equation (1) and get your answer.


What I explained to you, is part of Physics. 
In this compact form it is necessary information for solving this kind of problems in Algebra.