The perimeter of an equilateral triangle is mc022-1.jpg units. which expression can be used to show the side length of one side of the equilateral triangle? mc022-2.jpg: each side length is mc022-3.jpg units. mc022-4.jpg: each side length is mc022-5.jpg units. mc022-6.jpg: each side length is mc022-7.jpg units. mc022-8.jpg: each side length is mc022-9.jpg units

The expression for the perimeter as well as the choices are not properly shown. Therefore, I cannot give you an exact answer.
However, I can help you with the concept.

In an equilateral triangle:
1- All sides are equal 
2- All angles are equal

The perimeter of any triangle can be calculated as follows:
perimeter = first side + second side + third side

Since the three sides of an equilateral triangle are equal and assuming that each has a length of s units, the perimeter would be:
perimeter = s + s + s
perimeter = 3s

Now, if we are given the perimeter and we want to get the side length. all we have to do is divide the perimeter by 3.

Examples:
1- If the perimeter is 60:
side length = 60/3 = 20 units

2- If the perimeter is 6x + 15
side length = (6x+15) / 3 = 2x + 5 units

Hope this helps :)