Let's solve this probem in general, to understand the underlying concept.
The circumference of a circle, knowing its radius, is given by
[tex] C = 2\pi r [/tex]
So, if the radius is doubled, we map [tex] r \mapsto 2r [/tex] and the circumference becomes
[tex] C' = 2 \pi (2r) = 2 (2 \pi r) = 2C [/tex]
So, if you double the radius, the circumference doubles as well, and so it becomes
[tex] 22.75 \mapsto 45.5 [/tex]
