If the area of an equilateral triangle is

Area of equilateral triangle $=36 \sqrt{3} \mathrm{~cm}^{2}$

Area of equilateral triangle $=\left(\frac{\sqrt{3}}{4} \times a^{2}\right)$, where $a$ is the length of the side.

$\Rightarrow 36 \sqrt{3}=\frac{\sqrt{3}}{4} \times a^{2}$

$\Rightarrow 144=a^{2}$

$\Rightarrow a=12 \mathrm{~cm}$

Perimeter of a triangle = 3a

$=3 \times 12$

$=36 \mathrm{~cm}$