To solve a system of equations by elimination, we need to add or substract one equation to the other.
In this case, we can see that we have a single y in the two equations, then if we substract the first by the second, the y will be eliminated:
[tex]\begin{gathered} (-3x+y=18)-(-3x+y=18) \\ -3x-(-3x)+y-y=18-18 \\ 0=0 \end{gathered}[/tex]But, the two equations are equal, then we get a situation:
[tex]0=0[/tex]The solution is 0 = 0, or we say that the system has infinite many solutions. Also, this kind of systems are called dependant
