Please solve asap@!!!! Thanks

Dear student,
Mass of motor car, M=1200 kg
Initial velocity(u)=90km/h = 25m/s  [ As 1km/h =5/18 m/s]
time(t) = 4s ,final velocity(v)=18km/h = 5m/s
Acceleration(a)=(v-u)/t
 a= (5-25)/4=-20/4 = -5m/s² 
negative sign shows that it is retardation
change in momentum (Δp) = mv - mu = m(v-u)
 Δp = 1200 (25 - 5) = 24000 kgm/s
 External force required = Ma = (1200 kg)(-5m/s² ) = -6000N
Magnitude of force = 6000N
(-ve sign denotes direction of force is opposite to motion of car)
Regards.