Find the side length of an equilateral triangle, the perimeter of which is equal to the perimeter of a rectangle

Find the side length of an equilateral triangle, the perimeter of which is equal to the perimeter of a rectangle with sides of 5 cm and 1 cm.

Find the perimeter of the rectangle using the formula: P = 2 (a + b),
P = 2 (5 + 1) = 2 * 6 = 12 cm;
By the statement of the problem, the perimeter of the rectangle is equal to the perimeter of the triangle. So the perimeter of the triangle is 12 cm.
By the condition of the problem, the triangle is equilateral. The perimeter of an equilateral triangle is found by the formula: P = 3a.
Find the side of the triangle by substituting known measurements into the formula.
3a = 12;
a = 12: 3;
a = 4.
So the side of the triangle is 4 cm.
Answer: 4 cm.