The easiest way to solve these is to solve for the initial velocity (vi) before the acceleration (a)…unless you feel like doing it excessive algebra♀️
Given:
Vf=0m/s
t=15s
Δx=150m
So to solve for vi, we’re going to use the 2nd kinematic equation
Δx=1/2(vf+vi)t —> 2(150)-0/15= 20 m/s
Using this information, we can solve for the acceleration.
Vf=vi+at
a=vf-vi/t
0-20/15= -1.33 m/s^2
(Make sure you add the negative sign. The acceleration is negative because to car is slowing down)