We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{-3x} \cdot \left( 3x^2-5x \right) &= \color{blue}{-3x} \cdot 3x^2 + \color{blue}{-3x} \cdot \left( -5x\right) = \\ &= -9x^3+15x^2 \end{aligned} $$