If the length of one side of a rectangle is twice that of the other side, and its perimeter is 54 cm, then what is the length of the longer side of this rectangle?

18 cm

We know that,

Perimeter of rectangle = 2 ( l + b) 

We have,

Perimeter = 54 cm

⇒ According to the given Question,

 Length of the longer side = twice of breadth

Let the breadth be a

Then, length = 2a

= Perimeter = 2 (l +b) 

= 54 = 2( 2a + a) 

= 54 = 6a 

= a = 9

Hence, length of the longer side = 2a = ( 2 × 9) = 18 cm