in a group of 22 boys , 13 play basketball and 15 play football . 3 of the boys play neither . how many play both ?
18 boys play something . if b play both , then 13 + 15 - b = 18 answer is a
subtract(add(13, 15), add(subtract(subtract(22, 3), 15), subtract(subtract(22, 3), 13)))