Question

What was the average speed (in m/s) of a car that travels 400 km in 4 hours?

Answer 1

1 km = 1000 m
400 km = 400·1000 m = 400000 m

and

1 h = 3600 s
4 h = 4·3600 s = 14400 s

so the average speed:

$V=\dfrac{400000}{14400}\,\dfrac{m}{s}\approx\boxed{27.78\,\dfrac{m}{s}}$