Answer:
54 cm
Step-by-step explanation:
Because the perimeter of the square is 81 cm, each of its sides will be 81 ÷ 4 = 20.25 cm.
When we divide the square into rectangles, two sides remain the same lengths, and two others are [tex]\frac{1}3[/tex] their original lengths.
So the perimeter of each rectangle is
[tex]2*20.25+2*(20.25 \div 3)\\=40.5+13.5\\=54 (cm)[/tex]