I cant see all the question but this is how you find the derivative of your function using the product rule.
Here you use the extension of the product rule to 3 factors which we'll write as:-
f(x), g(x) and h(x):-
Derivative = f'(x) g(x) h(x) + f(x) g'(x) h(x) + f(x) g(x) h'(x)
(3x - 1)(x + 4)(2x - 1)
derivative = 3(x + 4)(2x - 1) + (3x + 1)(1)(2x - 1) + (3x - 1)(x + 4)(2)
= 3(x + 4)(2x - 1) + (3x + 1)(2x - 1) + 2(3x - 1)(x + 4)