Determine whether Rolle's Theorem can be applied to f on the closed interval [a, b]. (Select all that apply. ) f(x) = x2 − 4x − 21 x + 6, [−3, 7] Yes. No, because f is not continuous on the closed interval [a, b]. No, because f is not differentiable in the open interval (a, b). No, because f(a) ≠ f(b) If Rolle's Theorem can be applied, find all values of c in the open interval (a, b) such that f′(c) = 0. (Enter your answers as a comma-separated list. If Rolle's Theorem cannot be applied, enter NA.) c =