#### Answer

$r=2.5$

#### Work Step by Step

$C=2\pi r;$ $C=15.7$
Substitute known values. (Let $\pi=3.14$)
$15.7=2(3.14)r$
Solve for $r$ by dividing both sides of the equation by $2(3.14)$:
$\dfrac{15.7}{2(3.14)}=\dfrac{2(3.14)r}{2(3.14)}$
$r=\dfrac{15.7}{2(3.14)}=2.5$