PLEASE HELP ME!!

Steve was asked to subtract (4x2 - 3x + 4) - (x2 + 7x - 2). His work is shown below.

(4x2 - 3x + 4) - (x2 + 7x - 2)

= 4x2 - 3x + 4 - x2 + 7x - 2

= 3x2 + 4x + 2


Part A:Explain what mistake Steve made while doing the problem.
Part B: What is the correct answer to the subtraction problem Steve was given?