Circumference of a circle is pi x diameter (full length of the circle)
you have the radius which is half, so youd need to double it go geth the diameter.
24x2=48
and then 3.14x48=150.72
It is 4 because the diameter is twice longer than the radius!
Hey, here's a pic of it ! hope this helps !
p.s., photomath is a good app for algebraic answers with work, you should check it out (: