An aircraft lands with an initial velocity of 85 m/s and decelerates at 9.0 m/s2 until it travels at 4.0 m/s.

(a) Calculate the distance travelled along the ground by the aircraft as it decelerates.
(b) How long does this deceleration take?
(First decide which equations to use)

vf^2=vi^2+2ad

a=-9.0m/s^2, vf=4.0m/s, vi=85m/s
solve for d.

for time
vf=vi+at