Jada walks up to a tank of water that can hold up to 10 gallons. When it is active, a drain empties water from the tank at a constant rate. When Jada first sees the tank, it contains 7 gallons of water. Three minutes later, the tank contains 5 gallons of water. At what rate is the amount of water in the tank changing? Use a signed number, and include the unit of measurement in your answer.

How many more minutes will it take for the tank to drain completely? Explain or show your reasoning.

How many minutes before Jada arrived was the water tank completely full? Explain or show your reasoning.
Explain in words.