2003 Pascal Problem 21

A straight one-way city street has 8 consecutive traffic lights. Every light remains green for 1.5 minutes, yellow for 3 seconds, and red for 1.5 minutes. The lights are synchronized so that each light turns red 10 seconds after the preceding one turns red. What is the longest interval of time, in seconds, during which all 8 lights are green?

\textbf{(A)}\ 10\quad \textbf{(B)}\ 15\quad \textbf{(C)}\ 20\quad \textbf{(D)}\ 25\quad \textbf{(E)}\ 30

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 Pascal contests here.