Question 435674
{{{s^2+ s^2 = 140^2}}}
==> {{{2s^2 = 19600}}}
<==> {{{s^2 = 9800}}}
==> {{{s = 70sqrt(2)}}} <---length of one side of the pen.
(This can also be gotten by simply dividing 140 by {{{sqrt(2)}}}.)

Because {{{A = s^2 = 9800}}}, the area of the pen is 9800 square meters.