The car at the time of the start of braking had a speed of 54 km / h. Find the braking distance

The car at the time of the start of braking had a speed of 54 km / h. Find the braking distance and braking acceleration if braking lasted 15 s

Let us assume that the body braked along the entire path with constant acceleration, then the body’s motion is equally slow, then:
a = V / t
Let’s translate V in m / s:
54000/3600 = 15m / s
a = 15/15 = 1m / s ^ 2
S = V ^ 2 / 2a = 54 * 54/2 = 1458m