Join the nous using -'s, -s' or ... of ....
We use -'s/s'/' for people, animals, time expressions and periods of time.
1) singular noun + 's 2) plural nouns + s'/'s 3) compound nouns + 's 4) without a noun + 's 5) time expression + 's 6) period of time + 's/s'
the boy's name the girls' jackets my father-in-law's car It's my mother's yesterday's newspaper five minutes' walk
We usually use ... of ... for things, ideas etc.
1) noun + of + noun 2) with some words + of
the name of the three the end of the month the front of the car
1) our teachers' books 2) my sister-in-law's son 3) the roof of the house 4) the cat's tail 5) John and Ann's sister 6) the cause of the accident 7) Gina's illness 8) the results of the study 9) last night's party 10) three weeks' holiday 11) Mike's cousin's wedding 12) the back of the room 13) an hour's drive 14) two days' salary 15) the lid of the box 16) the howling of the wind 17) the streets of London 18) Mr Nolan's daughter 19) my girlfriend's name 20) the owner of the company