1) 20 + 18 - 30
2) 70 - 56 + 16
3) 85 - 80 + 67
4) 92 - 72 + 35
5) 100 - (28 + 12)
6) 100 - (49 + 21)

Решу по шагам:

1. $20 + 18 - 30$
   $20 + 18 = 38$, $38 - 30 = 8$ → 8

2. $70 - 56 + 16$
   $70 - 56 = 14$, $14 + 16 = 30$ → 30

3. $85 - 80 + 67$
   $85 - 80 = 5$, $5 + 67 = 72$ → 72

4. $92 - 72 + 35$
   $92 - 72 = 20$, $20 + 35 = 55$ → 55

5. $100 - (28 + 12)$
   $28 + 12 = 40$, $100 - 40 = 60$ → 60

6. $100 - (49 + 21)$
   $49 + 21 = 70$, $100 - 70 = 30$ → 30