Two sides of a parallelogram are in the ratio 5 : 3.

Let the lengths of two sides of the parallelogram be $5 x \mathrm{~cm}$ and $3 x \mathrm{~cm}$, respectively.

Then, its perimeter $=2(5 x+3 x) \mathrm{cm}$

$=16 x \mathrm{~cm}$

$\therefore 16 x=64$

$\Rightarrow x=\frac{64}{16}$

$\Rightarrow x=4$

Other side $\Rightarrow(3 \times 4) \mathrm{cm}=12 \mathrm{~cm}$