7 * 3 − 7 = 7 * 2 = 14;
3 * 5 + 3 = 3 * 6 = 18;
2 * 7 − 5 = 14 − 5 = 9;
37 + 6 + 14 = 37 + (6 + 14) = 37 + 20 = 57;
5 + 25 + 18 = 30 + 18 = 48;
48 + 7 + 13 = 48 + (7 + 13) = 48 + 20 = 68;
2 * 8 = 16;
2 * 9 = 18;
9 * 2 = 18;
15 : 5 = 3;
18 : 9 = 2;
21 : 7 = 3.