A wheel has a diameter of 21 inches.

Approximately how far does it travel in 3 revolutions?

So each 1 revolution it travels the distance around the rim of the wheele aka circumference

circumference=pi times diameter

diameter=21

circunference=pi times 21 or 21pi

so distance=number of revolutions times circunference

number of revolutions=3

subsitute

distance=3 times 21pi

distance=63pi

answer is 63pi

or aprox pi to 3.14 and do 63 times 3.14=197.82

aprox 197.82 inches