1) x + 320 = 80 * 7
x + 320 = 560
x = 560 - 320
x = 240
Проверка: 240 + 320 = 560
560 = 560
2) x - 180 = 240 : 3
x - 180 = 80
x = 80 + 180
x = 260
Проверка: 260 - 180 = 80
80 = 80
3) 400 - x = 275 + 25
400 - x = 300
x = 400 - 300
x = 100
Проверка: 400 - 100 = 300
300 = 300
Ответ: 240; 260; 100