SUVAT equation we need here is:
where is the initial velocity, is the final velocity, is the displacement or position, and is the acceleration.
However, since we did not start on the ground, has to be modified by some constant. that is, we will use
where is the height we are when time, , is zero.
now , and
Now, after 4 seconds, the ball hits the ground, so it's height is zero.
So , since that is what is when