Let's see this original ewuation:
[tex]x-y=11[/tex]
1) Substitute 4 in for x: [tex]4-y=11[/tex]
2)Subtract 4 from both sides. This cancels out four. [tex](4-4)-y=11-4[/tex]
3)Cancel: [tex]-y=7[/tex]
4)Multiply both sides by negative 1:[tex]-1*-y=11*-1 \\ y=-11[/tex]
[tex]y=-11[/tex]
