The first step to simplifying this expression is to multiply each te in the parenthesis by 3x.
3x × 4[tex] x^{4} [/tex] - 3x × 5x
Now calculate the first product in this expression.
12[tex] x^{5} [/tex] - 3x × 5x
Calculate the second product in this expression.
12[tex] x^{5} [/tex] - 15[tex] x^{2} [/tex]
Since you cannot simplify this expression any further,, the correct answer to your question is 12[tex] x^{5} [/tex] - 15[tex] x^{2} [/tex].
Let me know if you have any further questions
:)