A train can travel 40% faster than a car. Both start from point A at the same…

When two vehicles cover the same distance but start and arrive together, use Time = Distance / Speed for each one separately, then equate total times: (the faster vehicle's moving time) + (its stoppage time) = (the other vehicle's undisturbed travel time).

Applying this to the given trip:

1. Let the car's speed be x kmph. Since the train is 40% faster, the train's speed is 1.4x kmph.

2. The car covers the 84 km distance without stopping, so its travel time is 84/x hours.

3. The train's moving time (excluding stops) for the same 84 km is 84/(1.4x) hours.

4. The train's total time equals its moving time plus the 15-minute (1/4-hour) stoppage: 84/(1.4x) + 1/4.

5. Since both start together and arrive together, the car's time equals the train's total time: 84/x = 84/(1.4x) + 1/4.

6. Multiply throughout by 1.4x: 84(1.4) - 84 = 0.25(1.4x), i.e. 117.6 - 84 = 0.35x.

7. So 33.6 = 0.35x, which gives x = 96.

Cross-check: at x = 96 kmph, the car's time is 84/96 = 0.875 hr = 52.5 minutes. The train's speed is 1.4 x 96 = 134.4 kmph, so its running time is 84/134.4 = 0.625 hr = 37.5 minutes; adding the 15-minute stop gives 37.5 + 15 = 52.5 minutes, exactly matching the car's time.

So the car's speed is 96 kmph.