In the first 3.1 s, the car accelerates with acceleration a from rest to a speed of 54 km/h = 15 m/s, so its acceleration is
15 m/s = a (3.1 s)
a = (15 m/s) / (3.1 s)
a ≈ 4.8 m/s²
So in this time, it travels a distance of
x = 1/2 (4.8 m/s²) (3.1 s)²
x = 23.25 m
For the remaining time, it moves at a constant 15 m/s, covering a distance x of
x = (15 m/s) t
for until it moves 75 m, which takes
75 m = (15 m/s) t
t = (75 m) / (15 m/s)
t = 5 s
So, the car travels a total distance of 98.25 m in 8.1 s.
