Answer:
-10
Explanation:
-3 + - 7 = - 10
When you have 2 numbers with the same sign, you add them together and carry the sign over.
Example
-4 + -9 just add 4 and 9, which is 13, and carry the sign over (which is a -) so
-4 + -9 = -13
Another example
4 + 9 add the 4 and the 9, which, again, is 13, and carry the sign over (which is a +) so
4 + 9 = 13
It's different if you are mixing signs in a problem.
Example:
4 + -9 = ? In this case we can re-write it as 4 - 9, since 9 is larger than 4 we know the answer will be negative. So, we can switch it, to make it easy and take -9 + 4 now it's easier to see the answer is -5.