We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{-5} \cdot \left( 4m^2-5m-8 \right) &= \color{blue}{-5} \cdot 4m^2 + \color{blue}{-5} \cdot \left( -5m\right) + \color{blue}{-5} \cdot \left( -8\right) = \\ &= -20m^2+25m+40 \end{aligned} $$