If the functions \( f(x)=\frac{x^{3}}{3}+2bx+\frac{ax^{2}}{2} \) and \( g(x)=\frac{x^{3}}{3}+ax+bx^{2} \), \( a \neq 2b \) have a common extreme point, then \( a+2b+7 \) is equal to:
\( 4 \)
\( 3 \)
\( \frac{3}{2} \)
\( 6 \)