The length of a rectangle is twice the side of a square and its width is 6 m greater than the side of the square. If the area of the rectangle is three times the area of the square.

Let side of square=$xcm$
Therefore,
Length of rectangle=$2x$
Breadth of rectangle=$x+6$
  $2x(x+6)=3x^2$
$=>2x^2+12x-3x^2=0$
$=>x^2+12x=0$
$=>x^2=12x$
$=>x=12$
Therefore,
Side of square=$12$cm
Length of rectangle=$2\times 12$
                               =$24cm$
Breadth of rectangle=$12+6$
                                =$18cm$