2020 AMC 8 Problem 13

Jamal has a drawer containing 6 green socks, 18 purple socks, and 12 orange socks. After adding more purple socks, Jamal noticed that there is now a 60\% chance that a sock randomly selected from the drawer is purple. How many purple socks did Jamal add?

\textbf{(A) }6 \qquad \textbf{(B) }9 \qquad \textbf{(C) }12 \qquad \textbf{(D) }18 \qquad \textbf{(E) }24

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