there are different methods to find the perimeter of a rectangle ;; 
perimeter is noting but the sum of all the sides / in other words ... the length of the overall boundary 
there is always an equation to find the perimeter of a shape 
and f the shape rectangle .... the equation is 2 ( l + b) 
noting but ..... 2 ( length + breadth ) or ( 2 × length ) + ( 2 × breadth )