35 + (72-2x) : 8 = 42  *8

280 + 72 - 2x = 336

-2x=336-280-72

-2x=-16

x=8

Проверка:

35 + (72-2*8) : 8 = 42

42=42

35 + (72 - 2x): 8 = 42

(72-2х):8=42-35

(72-2х):8=7

72-2х=56

-2х=56-72

-2х=-16

х=8