Find f' (x) and find the value(s) of x where the tangent line is horizontal. X f(x) = - (7x -6) 49x + 6 f' (x) = - - (7x - 6) Select the correct choice below and fill in any answer boxes in your choice. O A. The value(s) of x where the tangent line is horizontal is (Use a comma to separate answers as needed.) O B. The tangent line is never horizontal