A water tank fills through two pipes. Water flows in through one pipe at a rate of 25,000 gallons per hour and in through the other pipe at a rate of 45,000 gallons per hour. Water leaves the system at a rate of 60,000 gallons per hour.

There are 3 of these tanks, and each tank holds

1 million gallons. Each tank is half full. Water is entering and leaving a tank at the maximum amounts. Determine the number of hours, x, it will take to fill all 3 tanks one at a time.