We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{2x} \cdot \left( 3x^2-4x \right) &= \color{blue}{2x} \cdot 3x^2 + \color{blue}{2x} \cdot \left( -4x\right) = \\ &= 6x^3-8x^2 \end{aligned} $$