Mark M. answered 04/28/21
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
[f(x+h) - f(x)]/h = [3(x+h)2 - 4(x+h) + 1 - 3x2 + 4x - 1] / h
= [3x2 + 6xh + 3h2 -4x - 4h + 1 - 3x2 + 4x - 1] / h = (6xh + 3h2 - 4h) / h = 6x + 3h - 4
f'(x) = the limit of the expression above as h approaches zero = 6x - 4
So, f'(2) = 6(2) - 4 = 8.