### Use the doubles fact for addition.4 + 5 = _____

9

Step by Step Explanation:
1. Here we need to calculate the sum of 4 and 5.
Let us write 5 as 4 + 1 and use the doubles fact for addition.
We get, 4 + 5 = 4 + 4 + 1
= 8 + 1       [Using the doubles fact: 4 + 4 = 8 ]
= 9
2. We get, 4 + 5 = 9.