Answer
$$\frac{x^2-18x}{30x+12}$$
Work Step by Step
To simplify complex fractions, we generally simplify the numerator and the denominator first and then simplify the overall fraction. (This is not required, but it is generally easier.) Doing this, we find:
$$\frac{\frac{x-18}{3}}{\frac{10x+4}{x}}\\ \frac{\left(x-18\right)x}{3\left(10x+4\right)} \\ \frac{x^2-18x}{30x+12}$$
