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
How many more minutes will it take for the tank to drain completely?

1)  Gallons per minute change is -2/3 gallons per minute  since it decreases by 2 gallons in 3 minutes
 
2)  we have 5 gallons and lose 2/3 gallons per minute
 
(2/3 gal/minute)(x minutes) = 5 gallons
x = 5(3/2) = 15/2 = 7.5 minutes to drain the other 5 gallons
 
3)  There was 10 gallons when the tank is full
     That is 3 gallons more than the 7 gals there when Jada arrived.
     (2/3)(x) = 3
     x = 3(3/2) = 9/2 = 4 1/2 minutes
 
The tank was full 4 1/2 minutes before Jada arrived