imo B

12 each

let the larger side of the rectangle = x
smaller side = y

therefore, 2x + 2y = 18*sqrt2
or x+y = 9 sqrt2............................................eq1

diagonals of a square are equal

therefore, x = 2y...........................................eq2

plugging in eq 1

2y+y = 9 sqrt2
3y = 9 sqrt2
y = 3 sqrt2

y is the diagonal of a square, therefore the side of the square is y/sqrt2

or side of square = 3 sqrt2/sqrt2

or side of square = 3

Hence, perimeter of the square = 4(side of square)

4*3 = 12

Whats the OA?
I am also getting 12

imo: 12