The wheel of an engine of 300 cm in circumference makes 10 revolutions in 6 seconds. What is the speed of the wheel (in km/h)?

Answer: Option A

Circumference = One revolution
Distance covered in 10 revolutions = 300 * 10 = 3000 cm = 30 m
30 meters are covered in 6 seconds.
Speed of the wheel = $$\frac{30}{\text{6}}$$ = 5 m/s
5 m/s = $$\frac{5\times 18}{5}$$  = 18 km/h. [ To convert m/s to km/h, we use to multiply by factor $$\frac{18}{5}$$ ]