We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{-5t^3} \cdot \left( 6t^7-9t \right) &= \color{blue}{-5t^3} \cdot 6t^7 + \color{blue}{-5t^3} \cdot \left( -9t\right) = \\ &= -30t^{10}+45t^4 \end{aligned} $$