Quadratic Equation And Inequalities

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