2017 Gauss 8 Problem 19

In a group of seven friends, the mean (average) age of three of the friends is 12 years and 3 months and the mean age of the remaining four friends is 13 years and 5 months. In months, the mean age of all seven friends is

\textbf{(A)}\ 156\quad \textbf{(B)}\ 154\quad \textbf{(C)}\ 155\frac{1}{2}\quad \textbf{(D)}\ 157\quad \textbf{(E)}\ 155

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Gauss contests here.