The constant π is defined as the ratio of the circumference of a circle with respect to its diameter, mathematically:
π=C/d which can be rearranged to
C=πd
Since the diameter is equal to twice the radius of the circle, ie d=2r
C=2πr dividing both sides by 2π gives you:
r=C/(2π), the "spoke" in our problem is equal to the radius of a circle, and we are told that C=42in so:
r=42/(2π) in
r=21/π in
r≈6.68 in (to nearest hundredth of an inch)