Answer:
x+3x-15=13
4x=28
x=7
......
[tex]y = 3x - 15 \\ \\ to \: find \: x \: substitute \: y \: into \: 0\\ \\ 0 = 3x - 15 \\ - 3x = - 15 \\ divide \: both \: sides \:by \: - 3 \\ \\ x = 5[/tex]
