7. (5 points) There are two trains, with lengths of 125 meters and 115 meters, and speeds of 22 meters/second and 18 meters/second, respectively. The two trains are traveling towards each other. The time from when the fronts of the trains meet until the rear ends separate is $\qquad$ seconds.
【Solution】Solve: $(125+115) \div(22+18)$
$$
\begin{array}{l}
=240 \div 40 \\
=6 \text { (seconds); }
\end{array}
$$

Answer: It takes 6 seconds from when the fronts of the two cars meet until the rear ends separate. Therefore, the answer is: 6.