(a) The function \( f(x) \) is decreasing on the intervals \( (-6, -2) \), \( (3, 5) \), and \( (6, 7) \).
(b) The function \( f(x) \) is increasing on the intervals \( (-2, 3) \) and \( (5, 6) \).
(c) The function \( f(x) \) is concave up on the interval \( (4, 5) \).