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


Given (−2.67b + 11) − (3.71b − 15)
Step 1 −2.67b + 11 + −3.71b − 15
Step 2 −2.67b + −3.71b + 11 − 15
Step 3 (−2.67b + −3.71b) + (11 − 15)
Step 4 −6.38b + (−4)


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.