if B is the midpoint of AC, that means that B cuts AC in two equal halves, namely that AB and BC are identical twins.
[tex]\bf \boxed{A}\stackrel{4x - 2}{\rule[0.35em]{10em}{0.25pt}} B\stackrel{2x+4}{\rule[0.35em]{10em}{0.25pt}}\boxed{C} \\\\\\ 4x - 2 = 2x + 4\implies 2x-2=4\implies 2x = 6\implies x=\cfrac{6}{2}\implies x = 3 \\\\[-0.35em] ~\dotfill\\\\ \stackrel{AB~=~BC}{4(3)-2= \underline{10}}~\hfill \stackrel{AC = AB+BC}{\underline{10}+\underline{10}=20}[/tex]
