42+78= 120, * * * is the same as the total speed, so it is added because it is relative.

300/ 120=2.5, and the running time is 300 (satisfied)

30+ 15*2=60 minutes = 1 hour, and the time of stopover delay.

2.5+ 1=3.5, the answer is 6+3.5=9.5.

Meet at 9: 30 a.m.

Note: because both cars have stopped for 30 minutes, if this is not the premise, it cannot be counted like this.

We can consider the limit. No matter when two cars stop in the process of running, we assume that it stops for 30 minutes at first, and then runs again, equivalent conversion. This is easier to understand.