1) (820-100)/(4х-2)-33=7
720/(4х-2)=7+33
720/(4х-2)=40
4х-2=720:40
4х-2=18
4х=18+2
4х=20
х=20:4
х=5
2) 35×4-60÷(5x+2)=135
140-60:(5х+2)=135
60:(5х+2)=140-135
60:(5х+2)=5
5х+2=60:5
5х+2=12
5х=12-2
5х=10
х=10:2
х=5
3) 2500÷20+6×(x÷3-9)=155
125+6*(х:3-9)=155
6*(х:3-9)=155-125
6*(х:3-9)=30
х:3-9=30:6
х:3-9=5
х:3=5+9
х:3=14
х=14*3
х=42
4) (35-31)×(x÷2-11)+13=26
4*(х:2-11)=26-13
4*(х:2-11)=13
4х:2-44=13
2х-44=13
2х=13+44
2х=57
х=57:2
х=28,5