Решаем примеры по порядку:
$$20 + 18 – 30 = 38 – 30 = 8$$
$$70 – 56 + 16 = 14 + 16 = 30$$
$$85 – 80 + 67 = 5 + 67 = 72$$
$$92 – 72 + 35 = 20 + 35 = 55$$
$$100 – (28 + 12) = 100 – 40 = 60$$
$$100 – (49 + 21) = 100 – 70 = 30$$
Ответ: 8, 30, 72, 55, 60, 30.