the acceleration due to gravity is -9.81 m/s
thus we have:
with the initial condition, m/s and
now, let's find and
(by the way is the position function, is the velocity function and is the acceleration function)
since , we have:
we obtain the max height when
that is, when
plug that into the position function:
since , we have that here.
since we obtain the max height at , the max height is,
i think you can handle the rest
...by the way? have you done calculus? if not, the suvat equations are the way to go, forget everything i said and see here (note that these equations assume all initials are zero.