The length and breadth of the rectangle are in a ratio $3:1,$ and the breadth $=7\mathrm{cm}$. Find the perimeter of the rectangle.

According to the given ratio let the length of the rectangle be $3\mathrm{x} \mathrm{cm}$and breadth be $\mathrm{x} \mathrm{cm}$

The breadth is given to be, $\mathrm{x}=7$

So, the length $= 21\mathrm{cm}$

Therefore, the Perimeter is:

$= 2 \times (\mathrm{l}+\mathrm{b})$

$= 2\times (7+21)$

$= 2 \times 28$

$= 56 \mathrm{cm}$