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.