Is 15x3 - 20x2 - 5x prime or can it be factored?

I'm not sure if, for example, "15x3" is 15 times 3 or 15x^3. However, I can answer both questions.

(15 times 3) - (20 times 2) - 5x --> 45 - 40 - 5x --> 5 - 5x. A "5" can be factored out, which will then lead to the result 5(1-x) or -5(x-1)

15x^3 - 20x^2 - 5x --> 5x(3x^2 - 4x - 1) --> I think this is the farthest it can be factored. Unless you find a way to get any two numbers to be able to multiply to the number -3x^2 and add to the number -4x.