AMC 8 2007 Problem 10

For any positive integer $n$, define $\boxed{n}$ to be the sum of the positive factors of $n$. For example, $\boxed{6} = 1 + 2 + 3 + 6 = 12$. Find $\boxed{\boxed{11}}$ . $\textbf{(A)}\ 13 \textbf{(B)}\ 20 \textbf{(C)}\ 24 \textbf{(D)}\ 28 \textbf{(E)}\ 30$