Answer:
x + y = 0
Explanation:
The problem states that variables x and y are the same distance away from 0 on the number line. Since x is at 4, it is 4 units away from 0. Assuming that x and y cannot be the same number, y would have to be at -4, because that is the only other number besides 4 that is 4 units away from 0.
If x and y can be the same number another possibility would be that y is also 4 making x + y = 8.