If the functions f(x)=x^3/3+2 b x+(a x^2)/2 and g(x)=x^3/3+a x+b x^2, a ≠ 2 b have a common extreme point, then a+2 b+7 is equal to:

If the functions $\displaystyle f(x)=\frac{x^3}{3}+2 b x+\frac{a x^2}{2}$ and $\displaystyle g(x)=\frac{x^3}{3}+a x+b x^2, a \neq 2 b$ have a common extreme point, then $\displaystyle a+2 b+7$ is equal to: