If Rolle's theorem holds for the function f(x)=2 x^3+ b x^2+ c x, x ∈[-1,1], at the point x=1/2, then 2 b + c equals:

If Rolle's theorem holds for the function $\displaystyle f(x)=2 x^3+\mathrm{b} x^2+\mathrm{c} x, x \in[-1,1]$, at the point $\displaystyle x=\frac{1}{2}$, then $\displaystyle 2 \mathrm{~b}+\mathrm{c}$ equals :