Let α, β, γ be the three roots of the equation x^3+b x+c=0. If β γ=1=-α, then b^3+2 c^3-3 α^3-6 β^3-8 γ^3 is equal to

Let $\displaystyle \alpha, \beta, \gamma$ be the three roots of the equation $\displaystyle x^3+b x+c=0$. If $\displaystyle \beta \gamma=1=-\alpha$, then $\displaystyle b^3+2 c^3-3 \alpha^3-6 \beta^3-8 \gamma^3$ is equal to