Panama Canal Locks on the Panama Canal are used to move a ship from a higher elevation to a lower elevation. When a ship enters a lock
chamber on the canal, water is allowed to spill out of the lock chamber
into the next lock chamber until the water levels in the two chambers
are equal. Suppose the water level in one lock chamber is 72 feet. As
water spills out of the chamber, the depth changes at a rate of about
-31 feet per minute until the water level is 41 feet. How many minutes
does it take for the depth to change from 72 feet to 41 feet?