The side of big square is 10 feet.
The area of square is
[tex]A=a^2[/tex]
Hence the area is
[tex]A=10\times10=100[/tex]
The side of the small sqaure is 5 feet.
Its area is
[tex]B=5\times5=25[/tex]
Hence the area of remaining portion is 100-25=75.
The answer is 3) 75 ft^2.
