I'm going to make this longer than it needs to be, so feel free to skim.

Remember that velocitygenerally speakingis the derivative of displacement, and that acceleration is the derivative of velocity. There's probably some more information they gave you in your textbook or wherever you found this problem concerning the downward acceleration due to gravity. Someone correct me if my constants are wrong, but I believe gravity exerts an acceleration of . So let's take a look at the different functions laid out (Assuming positive indicates upward direction relative to ground):

Acceleration:

We can integrate this to find velocity:

You already have been given the initial value of velocity, 42ft/sec:

The ball will achieve maximum height when the initial velocity is finally canceled out by the downward acceleration due to gravity. Simply find when it'snet velocityis zero to find the time of maximum height, and then plug that value into your formula for position (which can be found by integrating the velocity function and plugging in your initial height in for C, which should be zero).