A circle has radius 12. What is the area of a sector with a central angle of 60°?

A sector is a fraction of the whole circle, and that fraction is the central angle over $360°$. Here it is $\frac{60}{360} = \frac{1}{6}$. The full circle's area is $\pi r^2 = \pi (12)^2 = 144\pi$. So the sector area is $\frac{1}{6} \cdot 144\pi = 24\pi$, choice B. Choice A ($12\pi$) is the radius times $\pi$, which does not correspond to any area formula here. Choice C ($48\pi$) comes from using $\frac{1}{3}$, which would be a $120°$ sector. Choice D ($144\pi$) is the area of the entire circle, forgetting to take the fraction.