The answer is -13
After you add the -13 to both sides, you end up with:
-n = 13
When you rewrote the problem, you got rid of the negative sign on the n variable, making it positive. If you kept the negative sign, you end up with -13 as a final result because you need to find n, not negative n.
Thus,
n = -13
Summary:
Your mistake was that you got rid of the negative sign on the n, changing the problem's answer.
:)
