For a circle, the equation of the circumference is c = π * 2r (radius). Since in this case, the circumference is 15.3, that means π * 2r = 15.3. I'm going to assume that pi is 3.14 because the four answers aren't particularly close to each other. This means that 2r = approx. 4.872. If you then divide both sides by 2 you get r = approx. 2.436, which is closest to answer D.
