`a, 11 . (x - 9) = 77`
$\Rightarrow$ `(x - 9) = 77 : 11`
$\Rightarrow$ `x - 9 = 7`
$\Rightarrow$ `x = 7 + 9`
$\Rightarrow$ `x = 16`
$\text{Vậy}$ `x = 16`
____________________
`b, 2x - 45 = 5 . 3^{2}`
$\Rightarrow$ `2x - 45 = 5 . 9`
$\Rightarrow$ `2x - 45 = 45`
$\Rightarrow$ `2x = 45 + 45`
$\Rightarrow$ `2x = 90`
$\Rightarrow$ `x = 90 : 2`
$\Rightarrow$ `x = 45`
$\text{Vậy}$ `x = 45`
____________________
`c, 25 + 3 . (x - 8) = 106`
$\Rightarrow$ `3 . (x - 8) = 106 - 25`
$\Rightarrow$ `3 . (x - 8) = 81`
$\Rightarrow$ `(x - 8) = 81 : 3`
$\Rightarrow$ `x - 8 = 27`
$\Rightarrow$ `x = 27 + 8`
$\Rightarrow$ `x = 35`
$\text{Vậy}$ `x = 35`
