Answer
$$=3x^3-10x^2-51x+18$$
Work Step by Step
We first multiply the first two factors to get a total of two factors overall. Next, multiplying each term in the first factor by each term in the second factor, we find:
$$\left(x+3\right)\left(x-6\right)\left(3x-1\right) \\ \left(x^2-3x-18\right)\left(3x-1\right) \\ =3x^3-10x^2-51x+18$$