Please help with this question, step by step.

(5 points) (a) An urn contains 20 balls numbered 1 through 20. You then select 10 balls one by one, without replacement. What is the probability that the numbers on the 3rd, 5th, and 9th balls are increasing? (b) An urn contains 20 balls: 7 red balls, 4 black balls, and 9 green balls. You sample 10 balls Without replacement. What is the probability the 10th ball is black, given that the 8th and 9th balls are red