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=81.54

(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

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