When someone walks from a to B, there are regular buses between a and B, and the departure intervals between the two places are equal. He finds that a bus to a comes every 6 minutes, and a bus to B comes every 12 minutes. How many minutes does the bus leave from their respective departure station?

One in nine minutes, please give me some advice

When a bus arrives at a station, four out of seven passengers get off the bus and another 34 passengers come up. This is because the passengers on the bus are the original ones
How many people are there on the bus?

Get off at 4 / 7
And 1-4 / 7 = 3 / 7
After an increase of 34, it was 5 / 6
34÷(5/6-3/7)=84
A: there are 84 people on the bus