A half-gallon container of milk is tested by a quality control company. Let X be a rating of the milk quality, given as an integer from 1 to 10; let Y denote the exact volume of milk in the selected half-gallon container; let Z be "1" if the half-gallon of milk is 1% milkfat, or "2" if it is 2% milkfat, or "3" if it is fat-free, or "4" otherwise.