Consider the sequence of steps to solve the equation: 2(x − 4) + 6x = 9x − 10

given ⇒ 2(x − 4) + 6x = 9x − 10
step 1 ⇒ 2x − 8 + 6x = 9x − 10
step 2 ⇒ 2x + 6x − 8 = 9x − 10
step 3 ⇒ 8x − 8 = 9x − 10
step 4 ⇒ 8x − 8x − 8 = 9x − 8x − 10
step 5 ⇒ 0 − 8 = x − 10
step 6 ⇒ −8 = x − 10
step 7 ⇒ −8 + 10 = x − 10 + 10
step 8 ⇒ 2 = x + 0
step 9 ⇒ 2 = x

which step in solving this equation is justified by the commutative property of addition?
a) step 1 ⇒ 2x − 8 + 6x = 9x − 10
b) step 2 ⇒ 2x + 6x − 8 = 9x − 10
c) step 3 ⇒ 8x − 8 = 9x − 10
d) step 4 ⇒ 8x − 8x − 8 = 9x − 8x − 10