A drag racer starts from rest and accelerates uniformly for 5s covering a distance of 120 m.

a. what is the car's acceleration?
I did DI=vit+1/2at^2
120=0(5)+(.5)(5^2)a
120/12.5=12.5a/12.5
a= 9.6 m/s^2

b. what is the car's final velocity at the end of the 5s?
I did vf=vi+at
vf=0+9.6(5)
vf=48 m/s

c. at the end of the 120m track the driver opens a parachute and slams on his brakes. If he only has 30 m to bring his car to rest what acceleration will he experience? *****this part I'm lost at*****

appreciate the help!