14 is the initial amount of water.
12 pounds is what has left.
Use a ratio
8.345 pounds per 1 gallon equals 12 pounds per x gallons.
8.345/1=12/x
x=12/8.345
x=1.438 gallons
Subtract this number from the initial to get the remaining amount.
14-1.438=12.562
12.562 gallons of water are remaining.