Q: there are 8 red, 9 green and 6 yellow cards in a pack of cards. Five cards are drwan. Find the probability of obtaining 2 red and 3 green cards if it is known that at least one card is green

I don't get the restriction of the question "if it is known that at least one card is green"

the answer is , i don't get the part is the total number of ways of choosing 5 cards from 23, 14 is from 23-9,

1. I don't get the "at least" part and how it ties in with