6. When solving for the value of x in the equation, Martha wrote the following lines on the board.

Step 1 4(x - 1) + 3 = 18
Step 2 4(x - 1) = 15
Step 3 4x - 1 = 15
Step 4 4x = 16
Step 5 x = 4

Which property was used incorrectly when going from Step 2 to Step 3?

a. Addition Property of Equality
b. Distributive Property of Equality
c. Substitution Property of Equality
d. Transitive Property of Equality