Answer:
-4
You can break this down and make it more simple by doing so:
Start with 3 + (-13)
This is the equivalent of 3 -13 because when you add a negative it just means to subtract.
3-13 = -10
-10 - (-6)
When you minus a negative, it creates a positive, reversing the effect, effectively creating -10 + 6
-10 + 6 = -4
Hope that makes a bit of sense