IF he had done the first step correctly ( as it does not tell us what f(x) an g(x) is, then it should be the 3rd step, as he did not distribute the negative to all terms within the parenthesis.
3. 2x + 3x² - 5 - (-4x + 7)
2x + 3x² - 5 + 4x - 7
Combine like terms
3x² + 6x - 12 is your final answer
hope this helps
