1. 3 &#x000000d7&#x00000020&#x00000037 + 3

3 × 7 + 3 = 21 + 3 = 24
8 × 3 - 3 = 24 - 3 = 21
3 × 6 + 3 = 18 + 3 = 21
3 × 7 - 3 = 21 - 3 = 18