Forming possessive of nouns in English Grammar

To see if you need to make a possessive, turn the phrase around and make it an "of the..." phrase. For example:

the boy's hat = the hat of the boy
three days' journey = journey of three days

If the noun after "of" is a building, an object, or a piece of furniture, then no apostrophe is needed!
  1. room of the hotel = hotel room
  2. door of the car = car door
  3. leg of the table = table leg
Once you've determined whether you need to make a possessive, follow these rules to create one.
  1. add 's' to the singular form of the word (even if it ends in -s):
    the owner's car
    James's hat
  2. add 's' to the plural forms that do not end in -s: the children's game
    the geese's honking
  3. add ' to the end of plural nouns that end in -s: houses' roofs
    three friends' letter
  4. add 's' to the end of compound words: my brother-in-law's money
  5. add 's' to the last noun to show joint possessions of an object: Todd and Anne's apartment