Check the picture below.
since we know that x = 3/7, we can then plug that on either of the twin legs, since it's an isosceles, and get the length of each leg, so say let's plug it in 5x + 16
[tex]5x + 16\implies 5\left( \cfrac{3}{7} \right)+16\implies \cfrac{38}{7}+16\implies \cfrac{38+112}{7}\implies \cfrac{150}{7}\\\\[-0.35em]\rule{34em}{0.25pt}\\\\\stackrel{\textit{both legs}}{\cfrac{150}{7}+\cfrac{150}{7}}+\stackrel{\textit{base}}{6}\implies \cfrac{150+150+42}{7}\implies \cfrac{342}{7}\implies 48\frac{6}{7}\impliedby \textit{perimeter}[/tex]
