67. Two Trains. Two railway trains, one 400 feet long and the other 200 feet long, are moving on parallel tracks. When they move in opposite directions, each passes the other in 5 seconds, and when they move in the same direction, the faster one passes the other in 15 seconds. A curious passenger, using this data, managed to determine the speed of both trains.

Will the reader be able to find the correct answer? Of course, the trains are moving at a constant speed.
67. The relative speed of two oncoming trains is 600 feet in 5 s, or \(81 \frac{9}{11}\) miles/h. When the trains are moving in the same direction, their relative speed is 600 feet in \(15 \mathrm{s}\), or \(27 \frac{3}{11}\) miles/h. From this, we find that the speed of the faster train is \(54 \frac{6}{11}\) miles/h, and the speed of the slower train is \(27 \frac{3}{11}\) miles/h.