This isn't too bad. When a question asks for a negative plus a negative, just think of it as the negative minus a negative. -3-17. When you subtract two negatives, it's kinda like asking for adding two positives. The answer will be 20, not 14 as lots of folks mistake this part.
Now that we know -3-17, we have to add 13. This is adding a positive to a negative, so it's subtraction. -20+13. Same as asking 13-20. Which is -7.
Final answer: -7