Explanation:

Area of first square is =200

a^2  =200

a=10 √2

diagonal=√400

             =20 m

Diagonal  of second square=20 √2 

                 b^2  +b^2  =diagonal^2

               2b^2   =800

                  b^2=400  m^2

                   b=20 m

area of second square is=400