Question

Which property was used to simplify the expression? 3c+ 9 + 4c = 3c + 4c + 9

Answer 1

The change that happened from the first half of the equation to the second half was you moved the 9 and the 4c around.
Commutative property of addition allows you to do that. It's what says that 2+3 is the same thing as 3+2

Answer 2

B. 

Commutative, root word is commute- to move around. a+b+c = c+a+b
Associative deals with group (a+b)+c = (a+c)+b. 
Both of these pertain to only addition and multiplication. 

Distributive means to distribute the number outside of the parentheses to the numbers inside by multiplication or division. Only if the numbers inside are being added or subtracted

Inverse- Additive- equals zero. 2+(-2)=0
              Multiplicative- equals one. 9 * (1/9)=1