Two sides of a triangle measure 2x - 4 and 7x - 2 units, respectively. Which of these is a possible length for the third side of the triangle

Tough call if we don't know the perimeter of the triangle or anything else.

If, just if, the triangle is a right triangle and the given measurements measure the 2 shorter sides of the right triangle, then the length of the 3rd side (the hypotenuse) would be sqrt ([2x-4]^2 + [7x-2]^2). You should multiply out both squares and combine like terms here.

The answer here would be 6x.