Jika fungsi f(x)=ax+b+2 dan g(x)=ax-4 memenuhi f(f(x))=g(g(x)),maka ab+6a+b=

A(ax+b+2)+b+2 = a(ax-4)-4
a²x+ab+2a+b+2 = a²x-4a-4
ab+2a+b+4a = -4-2
ab+6a+b = -6