If a wheel makes a full turn, it will have traveled the entire distance around that wheel. After 3 revolutions, it should have traveled 3 times its circumfrence.
The circumfrence of a circle is equal to the diameter times pi. (about 3.14)
21 × 3.14 = 65.94 = circumfrence = 1 revolution
3 revolutions = = 65.94 × 3 = D. 197.82 in.
