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


Given (−3.12b + 12) − (4.36b − 11)
Step 1 −3.12b + 12 + (−4.36b) + 11
Step 2 −3.12b + −4.36b + 12 + 11
Step 3 (−3.12b + −4.36b) + (12 + 11)
Step 4 7.48b + 23


Part A: Identify and explain the first step where Margie made an error. (6 points)

Part B: Explain how to correctly write the expression in fewest terms by correcting the error in Part A. Show all work. (6 points)