First, let's find out when Bus 2 catches up to Bus 1. Bus 1 has a head start. By the time Bus 2 leaves, Bus 1 has already driven for 6 hours at 50 km/h. Therefore, it's 300 km down the road.
Now Bus 2 is chasing Bus 1, closing the gap at a rate of 80 - 50 = 30 km/h. To close a 300 km gap at 30 km/h, it will take:
300 ÷ 30 = 10 hours.
So, Bus 2 catches Bus 1 10 hours after Bus 2 leaves. This means it's 16 hours after Bus 1 left since Bus 2 left 6 hours late (6 + 10 = 16).
Here’s the important point: the problem states that Bus 3 catches up to Bus 1 at the same time as Bus 2 does. Thus, Bus 3 also catches Bus 1 at hour 16 (measuring from when Bus 1 left).
By then, how far has Bus 1 traveled? At the 16-hour mark, Bus 1 has gone:
50 × 16 = 800 km.
Now let's determine when Bus 3 left. If we say Bus 3 leaves x hours after Bus 1, then Bus 3 has been driving for (16 - x) hours when it catches up.
Since Bus 3 travels at 100 km/h, it needs to cover the same 800 km to catch Bus 1:
100 × (16 - x) = 800.
Divide both sides by 100:
16 - x = 8.
This shows that x = 8.
So, Bus 3 leaves 8 hours after Bus 1. Option
CWe can do a quick check: If Bus 3 leaves at hour 8, it drives for 16 - 8 = 8 hours before catching up, covering 100 × 8 = 800 km. This matches Bus 1's distance at hour 16 (50 × 16 = 800 km).