Find the parameter of the square with 25mm side.

Imagine a square first. The property, about the equality of all its sides, will help solve the problem. If we know the length of one side of the square, then this is enough to find the perimeter.
Now let’s remember what needs to be done to calculate the perimeter?
To do this, add the lengths of all sides of the square.
As a result, a record will appear: (25 + 25 + 25 + 25) mm, or you can use a more convenient way to find the perimeter of the square: 25 * 4 = 100 (mm) = 10 (cm).
Answer: 10 cm is the perimeter of the square.