The numbers of students in the four sixth-grade classes at northside school are 26,19,34 and 21. use properties to find the total number of students in the four classes.

Basically there are 3 addition properties and they are associative property, identity property, and commutative property. 

Commutative property is just changing the order of the addends. Example: 26+19+34+21= 21+34+19+26

Identity Property is just adding a 0 to the number that doesnt change anything. Example: 26+19+34+21 +0 = 100

Associative property is just changing the grouping of the addends. Example: (26+19) + (34+21) 

The answer should be c.