21. 7 - 2 + 9 = 14 8 - 5 + [] = 11 9 - 7 + [] = 12 10 - 6 + [] = 13 10 - 8 + [] = 11

Решим уравнения:

8 - 5 + x = 11

3 + x = 11

x = 11 - 3

x = 8

9 - 7 + x = 12

2 + x = 12

x = 12 - 2

x = 10

10 - 6 + x = 13

4 + x = 13

x = 13 - 4

x = 9

10 - 8 + x = 11

2 + x = 11

x = 11 - 2

x = 9

Ответ: 8, 10, 9, 9