Which property is not used to simplify the following expression?

2 x (x+5) + 7x = (2x + 10) + 7x
= (10 + 2x) + 7x
= 10 + (2x + 7x)
= 10 + 9x
=9x + 10

a. distributive property
b. commutative property of multiplication
c. associative property of addition
d. commutative property of addition