[tex]\bf \boxed{A}\stackrel{x+5}{\rule[0.35em]{10em}{0.25pt}} B\stackrel{2x-11}{\rule[0.35em]{10em}{0.25pt}}\boxed{C} \\\\\\ AB=BC\implies x+5=2x-11\implies 5=x-11\implies \blacktriangleright 16=x \blacktriangleleft \\\\\\ AB\implies x+5\implies 16+5\implies 21[/tex]
recall that a midpoint cuts two sections into equal twins.
