Suppose that X ~ N(3.2, 6.5), Y ~ N(-2.1, 3.5), and Z ~ N (12.0, 7.5) are independent random variables. Find the probability that
(a) X + Y ≥ 0
(b) X + Y - 2Z ≤ -20
(c) 3X + 5Y ≥ 1
(d) 4X - 4Y + 2Z ≤ 25
(e) |X + 6Y + Z| ≥ 2
(f) |2X - Y - 6| ≤ 1