$\text{a) 180 - 2.(x - 15) = $2^3$.5.}$
$\text{⇒ 180 - 2.(x - 15) = 8.5.}$
$\text{⇒ 180 - 2.(x - 15) = 40.}$
$\text{⇒ 2.(x - 15) = 180 - 40.}$
$\text{⇒ 2.(x - 15) = 140.}$
$\text{⇒ x - 15 = 140 ÷ 2.}$
$\text{⇒ x - 15 = 70.}$
$\text{⇒ x = 70 + 15.}$
$\text{⇒ x = 85.}$
$\text{Vậy x = 85.}$
$\text{b) [(6x - 39) ÷ 7].4 = 12.}$
$\text{⇒ (6x - 39) ÷ 7 = 12 ÷ 4.}$
$\text{⇒ (6x - 39) ÷ 7 = 3.}$
$\text{⇒ 6x - 39 = 3.7.}$
$\text{⇒ 6x - 39 = 21.}$
$\text{⇒ 6x = 21 + 39.}$
$\text{⇒ 6x = 60.}$
$\text{⇒ x = 60 ÷ 6.}$
$\text{Vậy x = 10.}$
$\text{c)10x - $2^3$.5 = $10^3$ ÷ $10^2$.}$
$\text{⇒ 10x - 8.5 = 10.}$
$\text{⇒ 10x - 40 = 10.}$
$\text{⇒ 10x = 10 + 40.}$
$\text{⇒ 10x = 50.}$
$\text{⇒ x = 50 ÷ 10.}$
$\text{Vậy x = 5.}$
