It will take 7.5 s for the car to stop.
One of the acceleration formulas is
[tex] v_{f} = v_{i} [/tex] +at, where
[tex] v_{f} [/tex] is the final velocity,
[tex] v_{i} [/tex] is the initial velocity,
a is the acceleration, and
t is the time.
0 = 30.0 m·s⁻¹ + (-4.0 m·s⁻²)t
4.0 s⁻¹ t = 30.0
t = [tex] \frac{30.0}{ 4.0 \text s^{-1}} [/tex]= 7.5 s
