$4.(\frac{1}{12})$ $+$ $10.\frac{1}{x}$ $=$ $1$
$ĐK$ $x$ $\neq$ $0$
$⇔$ $\frac{1}{3}$ $+$ $\frac{10}{x}$ $=$ $1$
$⇔$ $\frac{x}{3x}$ $+$ $\frac{30}{3x}$ $=$ $1$
$⇔$ $\frac{x+30}{3x}$ $=$ $\frac{3x}{3x}$
$⇔$ $\frac{-2x}{3x}$ $=$ $\frac{-30}{3x}$
$⇔$ $-2x$ $=$ $-30$
$⇔$ $x=15$