By the conditions the inlet takes 2 hours. That means the rate is .
The outlet takes 5 hours. That means the rate is
The tank is half full it has . The net gain from the two pipes is
gallons per hour.
Thus, the question is how long does it take for the net chain to reach gallons?
The answer is, hours.
Combine the denominator,
hours. Which is 1 hour and 40 minutes.