Answer
$(a)~r=240$ in
$(b)~d=480$ in
Work Step by Step
We know that the circumference of a circle is given by the formula:
$Circumference=2\pi~radius$
$C=2\pi r$
We can solve for the radius, $r$:
$r=\frac{C}{2\pi}$
We plug in $C=480\pi$ in:
$r=\frac{480\pi}{2\pi}$
$r=240$ in
(b) We know that the diameter relates to the radius by the formula:
$diameter=2*radius$
$d=2r$
We plug in $r=240$:
$d=2*240=480$ in
