1) 18 + 4 = 22; 89 − 6 = 83; 52 − 9 = 43; 30 − 7 = 23; 43 − 20 = 23; 31 + 40 = 71.
2) 54 + 36 = 90; 69 − 23 = 46; 37 + 46 = 83; 90 − 25 = 65.