х + (х + 170 + х - 120) = 1400
х + (2х + 50) = 1400
х + 2х + 50 = 1400
3х + 50 = 1400
3х = 1400 - 50
3х = 1350
х = 1350 : 3
х= 450
х + (х + 170 + х - 120) = 1400
х + (2х + 50) = 1400
х + 2х + 50 = 1400
3х + 50 = 1400
3х = 1400 - 50
3х = 1350
х = 1350 : 3
х= 450