Simplify \(\frac{900}{r}\times 360\) to \(\frac{324000}{r}\).
\[\frac{324000}{r}=72deg\]
Multiply both sides by \(r\).
\[324000=72degr\]
Divide both sides by \(72\).
\[\frac{324000}{72}=degr\]
Simplify \(\frac{324000}{72}\) to \(4500\).
\[4500=degr\]
Divide both sides by \(deg\).
\[\frac{4500}{deg}=r\]
Switch sides.
\[r=\frac{4500}{deg}\]
r=4500/deg
