A system of equations has infinitely many solutions. If 2y-4x=6 is one of the equations, which could be the other equation?

"infinity many solutions" implies that the two lines coincide.

Example:  starting with 2y-4x=6, I multiply every term by 3:  6y-12x=18

These two different-appearing equations are mathematically identical, so graphing both on the same set of axes results in two lines that coincide.