Answer:
Pi is about 3.14. Then the equation for circumfrance is 2(3.14)(R). Then you can first simplify that more to get an approximation of the circumference formula, which is 6.28R. Then you set that equal to the value of the given circumfrance, which is 28(3.14), or 87.92. So:
6.28R = 87.92.
Divide it all by 6.28 to get:
R = 14.
Radius equals to 14.