Ball thrown vertically upwards

if a ball is thrown vertically upwards with an initial speed of 20ms^-1 how do i show its maximum height and the time taken to reach this position in terms of g.

Also, if the origin is now taken to be the point of projection, and the unit vector i pointing vertically upwards, what will the force diagram look like under the quadratic model of air resistance?

I know that the acceleration at time t is a(t)i in which

a(t) = -g/b^2(v(t)^2+b^2), where v(t)i is the velocity of ball at time t, and b^2 = mg/0.2D^2.

However, how do i show this?

Cheers