We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{8x^4} \cdot \left( 4x-7 \right) &= \color{blue}{8x^4} \cdot 4x + \color{blue}{8x^4} \cdot \left( -7\right) = \\ &= 32x^5-56x^4 \end{aligned} $$