An equilateral triangle has a perimeter of 12 x + 18 units. Which expression can be used to show the length of one side of the triangle?
6 (2 x + 3): Each side length is 2 x + 3 units.
3 (4 x + 6): Each side length is 4 x + 6 units.
2 (6 x + 9): Each side length is 6 x + 9 units.
x (12 + 18): Each side length is 12 + 18 units.