<human>:  Bob is 75 miles ahead of Tom, driving 55 miles per hour. Tom is driving 70 miles per hour. How long will it take Tom to catch up with Bob?
<bot>: How fast is Tom driving? ** Tom is driving at 70 miles per hour to Bob's 55 miles per hour, meaning Tom is gaining at a rate of 70 mph - 55 mph = <<70-55=15>>15 mph.
How long will it take Tom to catch up with Bob? ** Bob is 75 miles ahead of Tom, and if Tom is gaining 15 mph on him, it will take Tom 75 miles / 15 mph = <<75/15=5>>5 hours to catch up with Bob.
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