Calculate the perimeter of a rectangle with sides 18 cm and 12 cm. How long will the side of a square with the same perimeter be?

Find the sum of the indicated sides of the rectangle.
18 + 12 = 30 cm.
Since the perimeter is the sum of all sides, and the opposite sides of the rectangle are equal, then its values will be:
2 * 30 = 60 cm.
A square has the same sides, so the length of its side will be equal to the ratio of the perimeter and 4 sides.
As a result, we get:
60/4 = 15 cm.
Answer: the length of the side of the square is 15 cm.