AMC 12 2017b Problem 1

Kymbrea's comic book collection currently has $30$ comic books in it, and she is adding to her collection at the rate of $2$ comic books per month. LaShawn's collection currently has $10$ comic books in it, and he is adding to his collection at the rate of $6$ comic books per month. After how many months will LaShawn's collection have twice as many comic books as Kymbrea's?

\textbf{(A)}\ 1 \textbf{(B)}\ 4 \textbf{(C)}\ 5 \textbf{(D)}\ 20 \textbf{(E)}\ 25