When Mr. Stanley's gas tank is full holds 15 gallons Mr. Stanley put 12 gallons of gas into the tank which filled it up how far was the gas tank before Mr. Stanley put 12 gallons in
3 gallons. If you subtract 12 from 15, it equals 3, which is how much the gas tank originally had. Add 12 to 3 and it would equal 15, making the tank full.
