Пошаговое объяснение:
a) (20-2х) ×7=28
20 - 2x = 28:7
20 - 2x = 4
2x = 20 - 4
2x = 16
x = 16 : 2
x = 8
б) (9х-15) ÷6=5
9x - 15 = 5 * 6
9x - 15 = 30
9x = 30+15
9x = 45
x = 45:9
x = 5
в) 72÷(6х+3) =8
6x + 3 = 72 : 8
6x + 3 = 9
6x = 9 - 3
6x = 6
x = 1
