6.2. Marlene has a fair die with the usual six sides. She throws the die and records the number. She throws the die again and adds the second number to the first. She repeats this until the cumulative sum of all the tosses first exceeds a prescribed number n.

(a) When n = 10, what is the probability that she stops at a cumulative sum of 13?

(b) When n is large, what is the approximate probability that she stops at a sum of n + 3?