Question 151277
Not sure how one would solve this without using algebra:) But will try to get it simple.

Tan left at 8 going 75. Chen caught up to him at 10. So when Chen passes Tan, Tan has been driving for 2 hours. He has gone 75*2 = 150km.

Chen reaches B in another 2 hours. But Tan is still 30km from town. Tan has driven another 2 hours since being passed by Chen, so Tan has driven another 150km. And he is till 30km from B. So the total distance between A and B is 150+150+30 = 330km.

1) The distance from when Chen passed Tan to B is 150+30 = 180.
Chen took 2 hours to cover 180km, so Chen's average speed is 180/2 = 90km.

2) The distance from A to where Chen catches Tan is 150km. Chen's average speed is 90. 150/90 = 5/3 hours. Chen left 20 minutes after Tan. So Chen left at 8:20