We know that the perimeter is at most 57 feet. We will call the length of each side with the variable 'x'. Each side is the same since it's an equilateral triangle.
The perimeter of the triangle is defined as '3x' because 3 times the side length of an equilateral triangle is its perimeter.
Since the perimeter is at most 57 feet, it can't be more than that. Therefore, we get the inequality 3x≤57.
This inequality is the same as saying the perimeter is less than or equal to 57 feet.
Now we solve.
3x≤57
Isolate 'x': 3x/3≤57/3
0<x≤19 is our answer.
The reason there is a "0<" added is because the side of a triangle can't be less than 0, that would be impossible.