两种1. (850-25)/(50+60)=7.5小时2. (850+25)/(50+60)=7.95小时
(850-25)/(50+60)=7.5(小时) 两车相遇之前 (850+25)/(50+60)=7又21/22(小时) 两车相遇之后
(850-25)/(50+60)=825/110=165/22小时