Which property is illustrated by the equation (a+b)+c=c+(a+b)

Associative property of addition Which property is illustrated by the equation (a+b)+c=c+(a+b) is the associative property of addition. The associative property of addition groups addends together which still yields the same sum regardless of the clustering or grouping set.
For example:
1.           1 + (2 + 3) = 6 = (1 + 2) + 3
2.           1 + (2 + 7) = 10 = (1 + 2) + 7
3.           550 + (20 + 5) = 575 = (550 + 5) + 20  

I’m confused as to what you are asking 66 2/3 percentage wise