A teacher received the following answer to a quiz question in which the student was asked to simplify the expression in Step 1:

Step 1: −4(x − 15y) + 5(−4x − 6y)
Step 2: −4x − 15y − 20x − 30y
Step 3: −4x − 20x − 15y − 30y
Step 4: (−4x − 20x) + (15y − 30y)
Step 5: −24x − 15y

Part A: Identify the step where the student made a mistake and explain the specific error that was made. Support your answer using the correct vocabulary. (6 points)

Part B: How would you correct the mistake? Show all your work. (6 points)