The number you need to add to -4 to get an answer of 9 is 13.
We can write this mathematically as:
-4 + x = 9
where x is the unknown number we need to find.
To solve for x, we can add 4 to both sides of the equation:
-4 + 4 + x = 9 + 4
Simplifying the left-hand side, we get:
x = 13
So the number we need to add to -4 to get 9 is 13.