3.6 gallons, If he buys 8.9 gallons of orange juice and he uses 5.3 gallons from it, he took away 5.3 from the 8.9 gallons so u do 8.9-5.3 u take the 9 and 3 first u get 6 then u add the decimal point and then subtract the 8 and 5 u get 3 so just combine them u get 3.6 gallons
