Because if your looking for probability, Its asking for the chance that it will be able to roll in a certain number so you have a 1/2 of it landing on one or the other side if it's a 2 sided coin or a 1/3 if you have a 3 sided triangle shaped dice.
60 minutes. Take how far it is above ground (20 m) and add it to the absolute value of how far it is below ground (340 m) to get 360 meters, which you divide by the rate of descent (6 m/min) to get 60 minutes.
