The distance from the main horse to the passenger horse and back is the same, so the time spent is the same. Yes (3/4- 1/3)/2=5/24 (days). So when the horse was overtaken, it left 1/3+5/24= 13/24 and left 300* 13/24. So the master's horse speed is (300* 13/24)/(5/24)=780 (Li). If you can understand the topic, it is not difficult to do it.