$1, (3x-6) \times 3 = 81$
$3x-6 = 81 : 3$
$3x - 6 = 27$
$3x = 27+6$
$3x = 33$
$x= 33:3$
$x = 11$
Vậy $x=11$
$2, 10 + 2 \times x = 16$
$ 2 \times x = 16 - 10$
$2 \times x =6$
$x = 6:2$
$x = 3$
Vậy $x=3$
$3, 2 \times x - 138 = 72$
$2 \times x = 72+138$
$2 \times x = 210$
$x = 210:2$
$x = 105$
Vậy $x=105$
$4, 71 + 65 \times 4 = \dfrac{x+140}{x} + 260$
$ 71 + 260 = 1 + \dfrac{140}{x} + 260$
$71 = 1+ \dfrac{140}{x}$
$\dfrac{140}{x} = 70$
$x = 140:7$
$x = 2$
Vậy $x=2$
$, 8,75 \times x + 1,25 \times x = 20$
$x \times (8,75+1,25) = 20$
$x \times 10 = 20$
$x = 2$
Vậy $x=2$.
