To solve the system, we have to combine the equations
[tex]\begin{gathered} x+3y=18 \\ x+3\cdot(-\frac{1}{3}x+6)=18 \\ x-x+18=18 \\ 0x=18-18 \\ 0=0 \end{gathered}[/tex]Given that the result is 0=0, we deduct that the system has infinitely many solutions.
