Each side of the square measures 6 cm.
The square has 4 sides.
The distance all the way around the square is (6 x 4) = 24cm
The equilateral triangle has the same perimeter as the square.
The distance all the way around the equilateral triangle is 24 cm.
A triangle has 3 sides, and in an equilateral triangle they're all the same length.
Each side = 1/3 of 24 cm = 8cm .