Answer:
The side of the square can be 13 or 9
Explanation:
Let x equal the unknown side of the rectangle and y equal the side of the square. The given information is that the area of the square is 4cm^2 larger than that of the rectangle. Mathematically this can be represented as

The second known is that their perimeters are equal so,

Solve the first equation in terms of x and substitute it into the second and you get the quadratic


Therefore your side length for the square can be either of those.