Variable $x$ cannot be equal to $0$ since division by zero is not defined. Multiply both sides of the equation by $4x$, the least common multiple of $x,4$.
$$4\times 10=x\times 12$$
Multiply $4$ and $10$ to get $40$.
$$40=x\times 12$$
Swap sides so that all variable terms are on the left hand side.
$$x\times 12=40$$
Divide both sides by $12$.
$$x=\frac{40}{12}$$
Reduce the fraction $\frac{40}{12}$ to lowest terms by extracting and canceling out $4$.
