2003 AMC 8 Problem 5

If 20% of a number is 12, what is 30% of the same number?

\mathrm{(A)}\ 15\qquad\mathrm{(B)}\ 18 \qquad\mathrm{(C)}\ 20 \qquad\mathrm{(D)}\ 24 \qquad\mathrm{(E)}\ 30

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.