Rule 4 - If a noun contains ‘o’ in the end of the word and before it there is a consonant then to make that plural we should add ‘es’. For example: Hero - Heroes , Mango - Mangoes.
Rule 5 - The noun which is in compound word, they have not hyphenated between the words then simply we add ‘s’ in the end of the noun. For example: Cupful - Cupfuls , Handful - Handfuls.
Rule 6 - Noun which is divided by hyphen, to make that plural we add ‘s’ in the important parts of the word. For example: Tooth- brush - Tooth - brushes, Pass- book - Pass - books.