Answer
`2x - 138 = 2^{3} . 3^{2}`
$\Rightarrow$ `2x - 138 = 8 . 9`
$\Rightarrow$ `2x - 138 = 72`
$\Rightarrow$ `2x = 72 + 138`
$\Rightarrow$ `2x = 210`
$\Rightarrow$ `x = 210 : 2`
$\Rightarrow$ `x = 105`
$\text{Vậy}$ `x = 105`
_____________________
`20 - [7 . (x - 3) + 4] = 2`
$\Rightarrow$ `[7 . (x - 3) + 4] = 20 - 2`
$\Rightarrow$ `7 . (x - 3) + 4 = 18`
$\Rightarrow$ `7 . (x - 3) = 18 - 4`
$\Rightarrow$ `7 . (x - 3) = 14`
$\Rightarrow$ `(x - 3) = 14 : 7`
$\Rightarrow$ `x - 3 = 2`
$\Rightarrow$ `x = 2 + 3`
$\Rightarrow$ `x = 5`
$\text{Vậy}$ `x = 5`
