On a recent exam, a student was asked to simplify the expression:

14(6x − 3y) − 2(10y + 8x)

Their work is shown below:
Step 1: 14(6x − 3y) − 2(10y + 8x)
Step 2: 84x − 42y − 20y − 16x
Step 3: 84x − 16x − 42y − 20y
Step 4: (84x + 16x) + (−42y − 20y)
Step 5: 100x − 62y

Part A: In which step did they make a mistake, and what was it? (2 points)

Part B: How would you correct the mistake and solve the problem? Show all of your work. (2 points)