5+х+21=3х+25
х-3х=25-5-21
-2х=-1
х=0,5
2х-12=2(10-7х)
2х-12=20-14х
2х+14х=20+12
16х=32
х=2
5х-12-2(х-1)=3(5-2х)+4х
5х-12-2х+2=15-6х+4х
5х-2х+6х-4х=15+12-2
5х=25
х=5
5+х+21=3х+25
х-3х=25-5-21
-2х=-1
х=0,5
2х-12=2(10-7х)
2х-12=20-14х
2х+14х=20+12
16х=32
х=2
5х-12-2(х-1)=3(5-2х)+4х
5х-12-2х+2=15-6х+4х
5х-2х+6х-4х=15+12-2
5х=25
х=5