Margie’s work for adding linear expressions is shown below. After checking her 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

Part B: Explain how to correctly write the expression in the fewest terms by correcting the error in Part A.