8. 8 + 4 +□ = 16 7 + 9 +□ = 20 9 + 0 +□ = 20 9 – □ + 15 = 15

1) $$8 + 4 + \boxed{4} = 16$$

2) $$7 + 9 + \boxed{4} = 20$$

3) $$9 + 0 + \boxed{11} = 20$$

4) $$9 – \boxed{0} + 15 = 15$$

Ответ: 4; 4; 11; 0