AMC 8 2020 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? $\textbf{(A) }6 \textbf{(B) }9 \textbf{(C) }12 \textbf{(D) }18 \textbf{(E) }24$