So I am looking at the method of elimination but I get a little bit lost why there is a positive +1 underneath the -1 , where does the +1 come from?

Answer:
it is because its being carried to the other side
Step-by-step explanation:
When you add 1 to negative 1 it becomes 0, so we are trying to make the right hand side equal to the left hand side. If that makes any sense.