The length of a rectangular park = 2(its breadth)
Perimeter = 840 m (Given)
Let x be the breadth of a rectangular park then, length of a rectangular park is 2x m.
We know, Perimeter of rectangle = 2(Length + Breadth)
840 = 2(Length + Breadth)
840 = 2(2x + x)
840 = 6x
or x = 140
Breadth = x = 140 m
and Length = 2x = 2 x 140 = 280 m
Area of a rectangular park = Length x Breadth = 140 x 280 = 39200 m2.