[tex]\begin{cases} \stackrel{\textit{1st side}}{a}\\[1em] \stackrel{\textit{2nd side}}{a + 4}\\[1em] \stackrel{\textit{3rd side}}{(a+4)+3} \end{cases}\qquad \stackrel{\textit{the perimeter or nam}\textit{ely their sum}}{(a)+(a+4)+[(a+4)+3] ~~ =~~101} \\\\\\ (a)+(a+4)+a+7=101\implies 3a+11=101\implies 3a=90 \\\\\\ a=\cfrac{90}{3}\implies a = 30~\hfill \stackrel{\textit{the 3rd side is}}{(30+4)+3\implies 37}[/tex]
