Answer:
Using the rules of arithmetic, we can simplify the given expressions as follows:
-8 - (-6) = -8 + 6 = -2
-3 - (-7) = -3 + 7 = 4
6 - (-7) = 6 + 7 = 13
-2 - (-15) = -2 + 15 = 13
-12 - 3 = -15
-4 - 12 = -16
9 - (-5) = 9 + 5 = 14
Therefore, the simplified expressions are:
-2, 4, 13, 13, -15, -16, and 14.