I am trying to understand a math problem. I realize it is pretty basic; but, here it is: x - (-6) = 12

According to the book I am reading the answer is:

x - (-6) = 12

x - (-6) + (-6) = 12 -6

x = 6

I, however, came up with a different answer and I can't figure out why I am wrong. I am hoping someone here can help me. My answer is:

x - (-6) = 12

x - (-6) + (+6) = 12 + 6

x = 18

Any help would be appreciated