Answer:
6 hours
Step-by-step explanation:
Since the trucks are moving in exactly opposite directions, the relative speed is 48 + 64 = 112 mph
If they have to be 672 miles apart, then the time taken is 672/112 = 6 hours
Check
After 6 hours, the truck traveling south would have covered 48 * 6 = 288 miles south
The truck traveling north would have covered 64 * 6 = 384 miles north
The distance between them after 6 hours would be 288 + 384 = 672 miles
