2х=3(2х+1)+5 7(2х+3)+х=4х-12 7х-3(4х-3)=7(3х+5)

2х=6х+3+5, 2х-6х=8, -4х=8, х=8:(-4), х= -2.
14х+21+х=21х+35, 14х+х-21х=35-21, -6х=14, х=14:(-6), х= -2.3.
7х-12х+9=21х+35, 7х-12х-21х=35-9, -26х=26, х=26:(-26), х= -1