First find the perimeter of rectangle.

The perimeter P of a rectangle is given by the formula, P = 2L + 2W

Where L is the length and is W is the width of the rectangle.

The perimeter P of a rectangle is

         (Substitute )

                           (Distributive property: a(b + c) = ab + ac)

                                             (Multiply: )

                                           (Distributive property: a(b + c) = ab + ac)

                                                      (Add: )

Next find the perimeter of square.

The perimeter P of a square is given by the formula, p = 2s

Where s is side length of the square.

The perimeter P of a square is

                (Substitute: s = 3x)

                   (Multiply:)

Write an equation that represents the situation.

So,

Substitute: ,    

       (Subtract 8x from each side)

                        (Additive inverse property: )        

                                    (Subtract: )

                               (Divide each side by 4)

                                    (Cancel common terms)

                                    (Divide:)

Check:

To check the solution, substitute in equations.   

Compare the values, the equation is true.

Dimension of rectangle:

Length of the rectangle,

Width of the rectangle,

Dimension of square:

Each side length of the square,

Length of the rectangle,

Width of the rectangle,

Each side length of the square,