13. Jamal has 6 green socks, 18 purple socks, and 12 orange socks in one of his drawers. After adding some purple socks, the probability of randomly drawing a purple sock from the drawer is $60 \%$. How many socks did Jamal add in total?
(A) 6
(B) 9
(C) 12
(D) 18
(E) 24
13. B.

When Jamal adds $x$ purple socks, there are $18+x$ purple socks in the drawer, so the total number of socks is $6+18+12+x=36+x$. This means the probability of picking a purple sock is $\frac{18+x}{36+x}$.
$$
\text { Hence } \frac{18+x}{36+x}=\frac{3}{5} \Rightarrow x=9 \text {. }
$$