Physics help!!?

Question

A ball is thrown vertically upward (assumed to be the positive direction) with a speed of 20.0 m/s from a height of 4.0 m.
(a) How high does the ball rise from its original position?
m
(b) How long does it take to reach its highest point?
s
(c) How long does the ball take to hit the ground after it reaches its highest point?
s
(d) What is the ball's velocity when it returns to the level from which it started?
m/s
show how you did it thanks

Answer 1

h=-4.9t^2+20t
h´=-9.8t+20=0 so t= 20/9.8=2.04s and
hmax=20.39m above the initial level
From the maximum height to ground the distance is 24.39 m and at maximum height the velocity is zero
so
24.39 =4.9t^2 m so t = sqrt(24.39/4.9)=2.23 s
v=-9.8t+20 m so at t= 4.08 s ( it takes the same time to go as to go down)
v= 40/9.8*(-9.8)+20 =-20m/s(the same velocity but directed downward)