Variable $x$ cannot be equal to $0$ since division by zero is not defined. Multiply both sides of the equation by $15x$, the least common multiple of $x,15$.
$$15\times 4+15x\times 20=x$$
Multiply $15$ and $4$ to get $60$.
$$60+15x\times 20=x$$
Multiply $15$ and $20$ to get $300$.
$$60+300x=x$$
Subtract $x$ from both sides.
$$60+300x-x=0$$
Combine $300x$ and $-x$ to get $299x$.
$$60+299x=0$$
Subtract $60$ from both sides. Anything subtracted from zero gives its negation.
$$299x=-60$$
Divide both sides by $299$.
$$x=\frac{-60}{299}$$
Fraction $\frac{-60}{299}$ can be rewritten as $-\frac{60}{299}$ by extracting the negative sign.
