Solve algebraically - x+y=4

You did not include instructions but I think you want to solve for y.

To do so, we isolate y.

Add 4 from both sides as step 1.

-y - 4 + 4 = 12 + 4

On the left side, - 4 and + 4 cancel out.

We now have this:

-y = 16

Next, divide both sides by - 1.

Final answer: y = - 16