We have the next formula to find the circumference of a circle
[tex]C=2\pi r[/tex]where C is the circumference and r is the radius
In our case we have
C= 28π
we substitute the value in the formula
[tex]28\pi=2\pi r[/tex]then we isolate the r
[tex]r=\frac{28\pi}{2\pi}=14[/tex]the radius is 14.