$\textit{Đáp án + Giải thích các bước giải:}$
$\text{a, 125 - 3(2x + 5) = 104}$
$\text{3(2x + 5) = 125 - 104 = 21}$
$\text{2x + 5 = 21 : 3 = 7}$
$\text{2x = 7 - 5 = 2}$
$\text{x = 2 : 2}$
$\text{x = 1}$
$\text{b, 90 - 2(4x + 1) = 80}$
$\text{2(4x + 1) = 90 - 80 = 10}$
$\text{4x + 1 = 10 : 2 = 5}$
$\text{4x = 5 - 1 = 4}$
$\text{x = 4 : 4}$
$\text{x = 1}$
$\text{c, 35 - (x + 5) = 16}$
$\text{x + 5 = 35 - 16 = 15}$
$\text{x = 15 - 5}$
$\text{x = 10}$
$\text{d, 127 - 9(x - 4) = 109}$
$\text{9(x - 4) = 127 - 109 = 18}$
$\text{9x - 36 = 18 }$
$\text{9x = 18 + 36 = 54}$
$\text{x = 54 : 9}$
$\text{x = 6}$
