Linear Motion problem

Wondering if im on the right track with below question



A body is projected vertically upwards from ground level with an initial velocity of 400m/s. determine;

(a) Time to reach the ground

(b) Velocity at a point 1.8km above the ground

(c) Time to reach a vertical height of 2.5km.





(a)

u=440m/s

v=0m/s

a=-9.81m/s



v=u+at

0=400+(-9.81)t

-400/-9.81=t

t=40.77sec



total time to reach ground 40.77*2=81.54sec



(b)



s=ut+1/2at²



s=400*40.77+1/2*(-9.81)*40.77²



s=1908 + (-8153.05)



s=-6245.05 m = 6.24km