Given, area of sector = \( \Large 72\pi cm^{2} \)

or \( \Large \frac{\pi r^{2}\theta}{360 degree}=72\pi \)

\( \Large \theta=\frac{72\times 360}{36\times 36} \)=> \( \Large \theta \)=20 degree

Now,length of arc

=\( \Large \frac{\pi r\theta}{180 degree}=\frac{\pi\times 36\times 20 degree}{180 degree}=4\pi cm \)