Not enough information has been given to answer the question. How fast is the helicopter going per mile?
That depends on your speed.
It depends on the helicopter and how it's being flown. If you have a Black Hawk helicopter and fly 100 miles in a straight line at full throttle, it'll take about half an hour to travel 100 miles. If you have a police helicopter and you creep along because you're looking for a car that ran off the side of a cliff, it's possible you won't go 100 miles all day.
That cannot be calculated without knowing the average speed over that distance.
2100/70 = 30 hours
150 hours
The maximum length is 1400 miles
1.46 days.
23.33333 hours
24.7058 hours
Time = Distance/Speed = 2100 miles / 85 mph = 24.71 hours.
About 28 hours.
That would be about 50 minutes.