Answer
$$\frac{3 x^2}{2 }.$$
Work Step by Step
We divide by the monomial as follows:
$$\frac{18x^{12}}{12x^4}=\frac{3\cdot 6x^6}{2\cdot 6x^4}=\frac{3 x^2}{2 }.$$
Note that we can not simplify any further, because "$2$" does not go into "$3$" evenly.
