Ответ:

1) (39 + x) - 84 = 78

39 + x = 78+84

х = 162 - 39

х = 123

(39 + 123) - 84 = 78

78 = 78

2) (x – 83) + 316 = 425

x – 83 = 425 - 316

х = 109 + 83

х = 192

(192 – 83) + 316 = 425

425 = 425

3) (600 – x) - 92 = 126

600 - х = 126 + 92

х = 600 - 218

х = 382

(600 – 382) - 92 = 126

126 = 126

Пошаговое объяснение: