`a, 12 + (5 + x) = 20`
$\Rightarrow$ `(5 + x) = 20 - 12`
$\Rightarrow$ `5 + x = 8`
$\Rightarrow$ `x = 8 - 5`
$\Rightarrow$ `x = 3`
$\text{Vậy}$ `x = 3`
______________________
`b, 175 + (30 - x) = 200`
$\Rightarrow$ `(30 - x) = 200 - 175`
$\Rightarrow$ `30 - x = 25`
$\Rightarrow$ `x = 30 - 25`
$\Rightarrow$ `x = 5`
$\text{Vậy}$ `x = 5`
_____________________
`c, 10 + 2x = 45 : 43`
$\Rightarrow$ `10 + 2x = 45/43`
$\Rightarrow$ `2x = 45/43 - 10`
$\Rightarrow$ `2x = -385/43`
$\Rightarrow$ `x = -385/43 : 2`
$\Rightarrow$ `x = -385/86`
$\text{Vậy}$ `x = -385/86`
_______________________
`d, 10x + 22 . 5 = 102`
$\Rightarrow$ `10 x + 110 = 102`
$\Rightarrow$ `10x = 102 - 110`
$\Rightarrow$ `10x = -8`
$\Rightarrow$ `x = -8 : 10`
$\Rightarrow$ `x = -4/5`
$\text{Vậy}$ `x = -4/5`
