A grandmother is knitting wool sweaters to donate to a non-profit organization. She knits pink and blue ones for girls and boys, respectively. It takes 3 balls of yarn to knit one. She has promised to donate 10 sweaters, but she has forgotten how many of the recipients are boys and how many are girls. So the grandmother decides to roll a 6-sided die to determine how many blue sweaters to knit. Let X be the number of the die (and, thus, the number of blue sweaters that she knits), and let Y = 10 - X be the number of pink sweaters that she knits.