Identical trains A and B are traveling non-stop on parallel tracks fro

Using the gap method in a "chase" scenario.

Train A, while traveling alone, creates the distance (gap) between the trains.

Train A travels alone for \(\frac{6}{5}\) hours
(r*t) = D (gap distance)
55 miles/hour * \(\frac{6}{5}\) hrs = 66 miles

At 6:12 p.m., both trains are moving.
This is the time at which the distance gap begins to get closed.
Train B travels faster than train A and will overtake A.

When travelers move in the same direction, subtract slower rate from faster rate to get the rate at which the gap shrinks (relative speed).
(66 - 55) = 11 mph

How long will it take for B to catch A?
D/r = t
D is 66. Relative rate, r, is 11.
66/11 = 6 hours

The clock time at which they are "exactly beside one another" is calculated from the time B leaves, which is when both trains are traveling and the gap begins to shrink.

Add 6 hours to 6:12 p.m., when B leaves
Train B catches Train A at 12:12 a.m.

Answer D