`ttcolor{orange}{@thuyhien}`

`1)` `9x - 7x = 80 + 4`

`x(9 - 7) = 84`

`2x = 84`

`x = 84 : 2`

`x = 42`

Vậy `x = 42`

`2)` `60 - 2x = 30`

`2x = 60 - 30`

`2x = 30`

`x= 30 :2`

`x= 15` 

Vậy `x = 15`