Let the breadth of the rectangular park be b.
∴ Length of the rectangular park = l = 2b
Perimeter = 840 m
\(\Rightarrow\) 840 = 2(l + b)
\(\Rightarrow\) 840 = 2(2b + b)
\(\Rightarrow\) 840 = 2(3b)
\(\Rightarrow\) 840 = 6b
\(\Rightarrow\) b = 140 m
Thus, we have:
l = 2b
= 2 x 140
= 280 m
Area = l x b
= 280 x 140
= 39200 m2