The solution is:
(x,y)= (0,4)
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[tex]\begin{gathered} \text{Let:} \\ x+y=7\text{ (1)} \\ y=6x\text{ (2)} \\ \text{ Replacce (2) into (1)} \\ x+6x=7 \\ 7x=7 \\ x=\frac{7}{7} \\ x=1 \\ \text{ Replace x into (2)} \\ y=6(1) \\ y=6 \end{gathered}[/tex]
