the wheel of a car is making 5 revolutions per second.if the diameter of the wheel is 84cm,find its speed.

Radius = 84/2 = 42 cm
Distance covered in one revolution = circumference of the wheel = $2\pi r=2*\frac{22}{7}*42=264cm$
Distance covered in 5 revolutions = 264*5=1320 cm in 1 second
Distance covered in 1 hour = 1320 * 3600=4752000 cm = 47.52 km=48 km(approcimately)
So the speed = 48 km /hour