## 245. Math Puzzle 10/85

Two trains pass each other while traveling in opposite directions. One at a speed of $36 \mathrm{~km} / \mathrm{h}$, the other at $45 \mathrm{~km} / \mathrm{h}$. A passenger in the second train noticed that it took 6 seconds for the first train to pass by him.

How long was the train that passed by him?