Question 379761
You were okay.

The key to doing this is to realize that when the ball reaches its maximum height, its velocity is ZERO.  We can then find the time it's in the air.

We know v(f) - v(i) = gt.  Here v(final) is zero and v(initial) is 100.  g = -32.

Therefore -100 = -32t and t = 3.125 seconds.