B. 14M
Start by finding the diameter; the formula for circumference is πd, so set up an equality:
28π=c
28π=πd
Divide both sides by π:
28ππ=πdπ
28ππ=πdπ
28=d
Diameter is twice as large as radius, so divide your diameter by 2 to get radius.
d2=r=282=14
Therefore, your radius is 14 units.