а. 10х-3х=84
7x = 84|:7
x = 12
б. (3х-12)+х=124
3x-12+x = 124
2x = 124+12
2x = 136|:2
x = 68
в. 5(6х+4)=230
30x +20 = 230
30x = 230-20
30x = 210|:30
x = 7
