Form the plural of a noun ending in y preceded by a vowel by adding -s adding -es changing the y to i and adding -s changing the y to i and adding -es

If I understand the question right I think an example would changing the singular word baby to the plural babies

Form the plural of a noun ending in y preceded by a vowel by adding -s.
Take the word play for example (play as in a drama text written by a playwright) - that word ends in -y and is preceded by a vowel A. Instead of adding -es, instead of changing y to i and then adding a suffix, you should simply add -s. There is no need to change anything (because of the vowel in front of Y).
So, the plural of play would simple be plays. 

Iam not sure sorry