$\text{a) 4x ÷ 17 = 0.}$
$\text{⇒ 4x = 0.17}$
$\text{⇒ 4x = 0.}$
$\text{⇒ x = 0.}$
$\text{Vậy x = 0.}$
$\text{b) 7x - 8 = 713.}$
$\text{⇒ 7x = 713 + 8.}$
$\text{⇒ 7x = 721.}$
$\text{⇒ x = 721 ÷ 7}$
$\text{⇒ x = 103.}$
$\text{Vậy x = 103.}$
$\text{c) 3x + 12 = 57.}$
$\text{⇒ 3x = 57 - 12.}$
$\text{⇒ 3x = 45.}$
$\text{⇒ x = 45 ÷ 3.}$
$\text{⇒ x = 15.}$
$\text{Vậy x = 15.}$