text: First, pour the eight quarts of water from the eight quart container into the radiator.  Then, pour the four quarts of anti-freeze from the four quart container into the "now empty" eight quart container.  Empty enough water from the radiator to continue filling the eight quart container, there will be four quarts left in the radiator, but the eight quart container will contain a 50% mixture.  Finally, empty the remaining four quarts of water from the radiator into the "now empty" four quart container, then pour the eight quarts of 50% mixture into the radiator.\n\nNow, you still need to put in four quarts of 50% mixture.  Pour the four quarts of water that is left into the eight quart container, then add another four quarts to make it a 50% mixture again, and mix well.  Pour half of that mixture into the radiator and you now have twelve quarts of 50% mixture in the radiator and four quarts of 50% mixture left over.