Answer:
associative property
Explanation:
we know that
According to the associative property of the sum, the sum of three or more numbers remains the same independently of how the numbers are grouped
so
![a+(b+c)=(a+b)+c](https://img.qammunity.org/2020/formulas/mathematics/middle-school/7hcr4n6g7nimvxzesnpe04b27nr2g7gej2.png)
In this problem we have that
----> by associative property of the sum