The radius is about 4.24 inches.
Work Step by Step
The apothem of a regular polygon forms a right triangle with half of a side and a radius. Since the apothem has a length of 3 and half of a side has a length of 3, it is a 45 45 90 triangle. r=a$\sqrt 2$ r=3$\sqrt 2$ r$\approx$4.24