Answer: 8 hours
Explanation:
Let x be the time before they meet ( in hours)
Speed of Sam = 12 mph
Sped of Fred = 9 mph
Distance = Speed × time
Distance covered by Sam in x hours = 12x
Distance covered by Fred in x hours = 9x
(Distance) (rate1) (time1) (rate2) (time2)
Total distance between them: 168 = 12 x + 9 x
Hence, the number of hours before they meet if Sam runs 12 mph and Fred runs 9 mph. = 8