Find f'(x) (the derivative of f(x)) if f(x) = 7x'3 - 2x'2 + 4x - 5.
Option A: 21x^2-4x+4+C
Option B: 21 x^2-4x+4-5
Option C: 21 x^2-4x+4
Option D: 21x^2-4x+4-5/x