It is going at a rate of 2000 ft every minute. So that is 2000 times every minute. Let setup an equation to solve this.
m = minutes
2000m = 50000
Lets solve for m, which is our minutes
2000m = 50000
m = 50000 / 2000
m = 25 minutes
It would take 25 minutes at a rate of 2000 ft/minute to reach 50000 ft
