If we want to isolate y, we can just simply add both sides by y.
After doing that, you get the following:
[tex]-y+y-x-1=y[/tex]
The two y's on the left side cancel each other out, so we are left with the following equation
[tex]-x-1=y[/tex]
Now, we have y isolated on the right side. I hope this helps! :)
~AgentCozmo4, Moderator