To solve the system of linear equations 3x-2y=4 and 9x-6y=12 by using the linear combination method, Henry decided that he should first multiply the first equation by –3 and then add the two equations together to eliminate the x-terms. When he did so, he also eliminated the y-terms and got the equation 0 = 0, so he thought that the system of equations must have an infinite number of solutions. To check his answer, he graphed the equations 3x-2y=4 and 9x-6y=12 with his graphing calculator, but he could only see one line. Why is this?