Question 436154
{{{x^2 + x^2 = 140^2}}} by the Pythagorean Theorem
{{{2x^2 = 19600}}}
{{{x^2 = 9800}}}
{{{x = 70sqrt(2)}}} meters, after taking square-roots.

Area of square pen is {{{A = x^2 = 9800}}} square meters.