[tex]x = y - 7 \\ 3x + 4y = 0 \\ \\ \\ 3(y - 7) + 4y = 0 \\ x = y - 7 \\ \\ 3y - 21 + 4y = 0 \\ x = y - 7 \\ \\ 7y = 21 \\ x = y - 7 \\ \\ y = 3 \\ x = - 4[/tex]