Perimeter of square = Perimeter of rectangle
=> 4(side) = 2(length + width)
=> 4(x+5) = 2[(x+3)+(x+7)]
=> 4(x+5) = 2[x+3+x+7]
=> 4x + 20 = 2x + 6 + 2x + 14
=> 4x + 20 = 4x + 20
=> 4x - 4x + 20 = 20
=> 20 = 20
So, any real number is the solution of this equation. It means that for every real number as x, the perimeter of the square will be same as the perimeter of the rectangle.
