what is y=13-x,solve for x

Answer 1

y=13-x
Add x to both sides.
y+x=13+x-x
combine terms
y+x=13
Now subtract y from both sides.
y-y+x = 13-y
combine terms
x=13-y

Answer 2

In order to solve for x, you must isolate the x. So try to get x on one side.