Algebra 1: Common Core (15th Edition)

Recall the following equation: $c=2\pi r$, where r is radius and c is circumference. We plug in the values given to obtain: $94.2=(2)(3.14)(r) \\\\ 94.2=6.28 \times r$. We simplify by dividing both sides of the equation by 6.28 to obtain that the radius is 15 mm.