The perimeter of a parallelogram is 140 cm. If one of the sides is longer than the other by 10 cm, find the length of each of its sides.

Let the lengths of two sides of the parallelogram be $x \mathrm{~cm}$ and $(x+10) \mathrm{cm}$, respectively.

Then, its perimeter $=2[x+(x+10)] \mathrm{cm}$

$=2[x+x+10] \mathrm{cm}$

$=2[2 x+10] \mathrm{cm}$

$=4 x+20 \mathrm{~cm}$

$4 x+20=140$

$\Rightarrow 4 x=140-20$

$\Rightarrow 4 x=120$

$\Rightarrow x=\frac{120}{4}$

$\Rightarrow x=30$

Length of one side $=30 \mathrm{~cm}$

Length of the other side $\Rightarrow(30+10) \mathrm{cm}=40 \mathrm{~cm}$