Hello from MrBillDoesMath!
Answer:
18
Discussion:
Imagine a fixed point on the wheel. The phrase "A bicycle wheel travels 36 pi inches " means that point has traveled 36 pi inches in 1 circumference. As C = 2 Pi r
C = 2 Pi *r = 36 Pi => divide both sides by 2 Pi
r = (36 Pi)\(2 Pi)
r = 18
Thank you,
MrB