If x is the side pf the square and d is the diagonal, using Pythagoras theorem, you can write 2*x^2 = d^2. D is given, Find x and perimeter which is 4x.

In the rhombus let o be the point of intersection of diagonals. In triangle RHO angle RHO = 30 degrees. If x is the side of the rhombus, OH = x*cos30. OH is given. Find x and perimeter which is again 4x.