ANSWER ASAP!!! WORTH 20!!

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


Given (−3.78b + 12) − (4.82b − 16)
Step 1 −3.78b + 12 + −4.82b − 16
Step 2 −3.78b + −4.82b + 12 − 16
Step 3 (−3.78b + −4.82b) + (12 − 16)
Step 4 −8.6b + (−4)


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)