Cookies are sold singly or in packages of 10 or 30. with this packaging, how many ways can you buy 60 cookies?

there is an answer on here but it is saying it is wrong.

For easier, let's say x represents a pack of 10 and y represents a pack of 30

we can start with 2 of the 30's
2y=60
we can replace one of the 30's with 3 of the 10's
y+3x=60

and finally we can use all 10's
6x=60

there are only 3 ways

It is 2 out of 8 she will pick green and 3 out of 7 she will pick green but red and green would be 5 out of 5 so 50% chance