There are three ways to find 18 small squares to make rectangles. ① The circumference of a row 18 squares is 76 decimeters.

②2 rows and 9 rows with a circumference of 44.

③3 rows and 6 rows with a circumference of 36.

the second question

The side lengths of the big square and the small square are 8 and 4 respectively.

Together, the circumference is 32+ 16-4-4 = 40.

Extended data

If it is a triangle with the same area, the perimeter of an equilateral triangle is the shortest; If it is a quadrilateral with the same area, the perimeter of the square is the shortest; If pentagons with the same area are used, the perimeter of regular pentagons is the shortest; If you use any polygon with the same area, the circumference of a regular circle is the shortest.

Perimeter can only be used on two-dimensional figures (planes and surfaces), and three-dimensional figures (solids) such as cylinders, cones and spheres can't express their boundary size by perimeter, but by total surface area.

Total surface area = the total area of all sides of a solid.