Margie's work for adding linear expressions is shown below. After checking her answer with the answer key, she solved it incorrectly.


Given (−4.23b + 13) − (5.47b − 12)
Step 1 −4.23b + 13 + (−5.47b) + 12
Step 2 −4.23b + −5.47b + 13 + 12
Step 3 (−4.23b + −5.47b) + (13 + 12)
Step 4 9.7b + 25


Part A: Identify and explain the first step where Margie made an error. (2 points)

Part B: Explain how to correctly write the expression in fewest terms by correcting the error in Part A. Show all work. (2 points)