Question

some on help me
In the following example of "Simplifying an Expression", what reason would be used for step B?

Simplify the expression 3k + 7 + 2k and justify each step

3k + 7 + 2k = 3k + 2k + 7 A
= open parentheses 3k + 2k close parentheses + 7 B
= open parentheses 3 + 2 close parentheses times k + 7 C
= 5k + 7 D
A. Addition
B. Commutative Property
C. Associative Property
D. Distributive Property