Answer :
[tex]x= \frac{1}{3}y[/tex] put all numbers on the left
[tex]x- \frac{1}{3}y=0[/tex]
third equation is the answer
[tex]x- \frac{1}{3}y=0[/tex] multiply by 3
3x-y=0
[tex]x- \frac{1}{3}y=0[/tex]
third equation is the answer
[tex]x- \frac{1}{3}y=0[/tex] multiply by 3
3x-y=0
[tex]x=\frac{1}{3}y\ \ \ \ \ \ \ \ \ |substract\ \frac{1}{3}y\ from\ both\ sides\\\\\boxed{x-\frac{1}{3}y=0}\\\\x-\frac{1}{3}y=0\ \ \ \ |multiply\ both\ sides\ by\ 3\\\\\boxed{3x-y=0}[/tex]