2010 AMC 10A Problem 5

Recall that the formula for the circumference of a circle is $2 \pi r.$ We then have that $$24\pi = 2\pi r$$$$r = 12.$$ The area of a circle is $\pi r^2,$ so we have that $$k \pi = \pi 12^2$$$$k = 144.$$ Thus, E is the correct answer.