Check the picture below.
[tex]\bf \textit{area of a regular polygon}\\\\ A=\cfrac{1}{2}ap~~ \begin{cases} a=apothem\\ p=perimeter\\[-0.5em] \hrulefill\\ A=70\\ a=5 \end{cases}\implies 70=\cfrac{1}{2}(5)p\implies 140=5p \\\\\\ \cfrac{140}{5}=p\implies 28=p[/tex]
