Find the length of the side of an equilateral triangle if its perimeter is 6 dm 9 cm

Let’s translate all units of measurement into one, for example, in centimeters, based on the fact that 1 dm = 10 cm: 6 dm 9 cm = 69 cm.
As you know, the perimeter of a triangle is the sum of all sides, and is calculated using the following formula: P = a + b + c.
In an equilateral triangle, all sides are equal, a = b, b = c, a = c, which means P = 3a.
Substitute all the known values of the sides of the triangle in the formula and find the perimeter: P = 69 * 3 = 207 cm.
Answer: the perimeter of an equilateral triangle, given the length of its side, is 207 cm or 20 dm 7 cm.