Maths problem, how to do?

(a) 
initial vel., u= 90 km h⁻¹ = 90*1000/60*60 ms⁻¹ = 25 ms⁻¹
final vel., v= 0 distance travelled, s=33.6 m 

v² - u² = 2as
0 - 25² = 2a(33.6)
∴ a = - 67.2/625 ms⁻²

∴ net force on the car 
= ma = 1800*67.2/625 kgms⁻² = 193.54 kgms⁻² (to 2 dec. pl.)

(b) If braking distance is halved, 
‬v² - u² = 2as 
0 - 25² = 2a(33.6/2)
∴ a = - (67.2/625)*2 ms⁻²
=> acceleration,a is doubled
=> net force on the car, ma is also doubled

So, net force on the car = 2*193.54 = 387.08 kgms⁻² (to 2 dec. pl.)

...........Induction device