now, if M is the midpoint of AB, that means that the halves of AM and MB are twins.
[tex]\bf \boxed{A}\underset{\leftarrow\qquad 6x-2\qquad \to }{\stackrel{4x+4}{\rule[0.35em]{10em}{0.25pt}} M\stackrel{4x+4}{\rule[0.35em]{10em}{0.25pt}}}\boxed{B} \\\\\\ AB=AM+MB\implies 6x-2=8x+8\implies 10=2x \\\\\\ \cfrac{10}{2}=x\implies 5=x \\\\[-0.35em] ~\dotfill\\\\ \stackrel{AB}{6(5)-2}\implies \blacktriangleright 28 \blacktriangleleft[/tex]