We can use distribution property to multiply the polynomial by the monomial.
$$ \begin{aligned} \color{blue}{2} \cdot \left( -3g^2-9 \right) &= \color{blue}{2} \cdot \left( -3g^2\right) + \color{blue}{2} \cdot \left( -9\right) = \\ &= -6g^2-18 \end{aligned} $$