Acar slows down from 23 m/s to rest in a distance of 85 m. what was its acceleration, assmed constant

First calculate the time by using following equation:
d= (vi+vf)/2 x t 

where t = time

vi is the initial velocity = 23 m/s

vf is the final velocity  = 0 m/s

and d is the distance covered = 85m

85 = (23 + 0)/2 x t

t = 85/11.5 = 7.39s

Now use this equation to find acceleration:

a= (vf-vi)/t 

a = 0 – 23/ 7.39

a = -3.112 m/s²

so, the acceleration is 3.112 m/s²

the device is called “ rocket engine”

so easy. just google the electromagnetic waves and it’ll pop up.