18 Years Old Algebra Equation Funny 18th Birthday Math Shirt Solid colors: 100% Cotton; Heather Grey: 90% Cotton, 10% Polyester; All Other Heathers: 50% Cotton, 50% Polyester Imported Machine wash cold with like colors, dry low heat Funny t-shirt for any 18 year old math nerd Great 18th birthday gift for anyone who enjoys a little math humor Lightweight, Classic fit, Double-needle sleeve and bottom hem