3 + 8 = 11 12 + 5 = 17 16 − 7 = 9 14 − 4 = 10 13 − 6 = 7 2 + 15 = 17   19 − 6 = 13 15 − 5 = 10 18 − 14 = 4 11 + 7 = 18 16 − 9 = 7 17 − 12 = 5