3 Three fair 6-sided dice, each with faces marked 1, 2, 3, 4, 5, 6, are thrown at the same time repeatedly. The score on each throw is the sum of the numbers on the uppermost faces. (a) Find the probability that a score of 17 or more is first obtained on the 6th throw. (b) Find the probability that a score of 17 or more is obtained in fewer than 8 throws. T [3] [2]​