Application Of Derivatives

If the functions $f(x)=\frac{x^3}{3}+2 b x+\frac{a x^2}{2}$


and $g(x)=\frac{x^3}{3}+a x+b x^2, a \neq 2 b$

have a common extreme point, then $a+2 b+7$ is equal to :