[tex]\ip ax + bx + 4x = 64 \Longleftrightarrow x(a+b+4) =64\ \ \ (*)[/tex]
[tex]\it x=2 \stackrel{(*)}{\Longrightarrow }2(a+b+4) =64|_{:2} \Longrightarrow a+b+4=32|_{-4} \Longrightarrow a+b=28[/tex]
[tex]\it m_a = \dfrac{a+b}{2} =\dfrac{28}{2}=14[/tex]
