Answer:
We would need to travel at 60 mph.
Step-by-step explanation:
If it takes 5 hours for a messenger to reach its destination at a speed of 42 mph, then the total amount of miles is 42x5 = 210 miles.
Now we know that we need to drive 210 miles in 3.5 hours.
Dividing 210/3.5, this gives us a total of 60.
Therefore, we would need to travel at a speed of 60 mph to reach our destination in 3.5 hours.