Two linear equations can have zero, one, or infinitely many solutions. Â Zero if the are parallel, have the same slope, and have different y-intercepts, one if they they have different slopes, infinite if they have the same slope and y-intercept (as they both describe the same line :P)
In this case if you factor the right side by three, you have the same exact expression as the left side. Â This means that each side represent the same line and has infinitely many solutions.