Hello!
Since this triangle is an equilateral triangle, then the length of each side of the triangle must be equivalent to one another.
(PΔ = side 1 + side 2 + side 3) and side 1 = side 2 = side 3
Since all triangles have 3 sides, we divide the perimeter of the triangle by 3, and then we will get the length of each side.
(6x + 15) / 2 = 2x + 5
Therefore, the length of each side of the triangle is 2x + 5.