Can someone please explain how to solve this problem?

Question

A bag contains 6 blue marbles, 10 red marbles, and 9 green marbles. If two marbles are drawn at random without replacement, what is the probability that two green marbles are drawn?

Answer 1

total marbles = 6 + 10 + 9 = 25

first draw 9/25
second draw 8/24
so
(9/25)(1/3) = 9/75