Answers in bold and underlined.
Answer 1: Es el coche *de mi amiga*. Es SU coche (de mi amiga).
Translation 1: It's *my friend's* car. It's HIS (my friend's) car.
Answer 2: Son los papeles *de mi*. Son MIS papeles.
Translation 2: They are the papers *of me*. They are MY papers.
Answer 3: No leo el blog *de ti*. No leo TU blog.
Translation 3: I don't read *your* blog. I don't read YOUR blog.
Answer 4: Son las letras *de ustedes*. Son SUS letras.
Translation 4: They are the lyrics *of you*. They are HIS letters.
Answer 5: Aquellos son los libros *de ellas*. Aquellos son SUS libros.
Translation 5: Those are the books *of them*. Those are HIS books.
Answer 6: Son las joyas *de mí*. Son MÍAS las joyas.
Translation 6: They are the jewels *of me*. The jewels are MINE.
Answer 7: Es el primo *de María*. Es el primo DE MARÍA.
Translation 7: He's *Maria's* cousin. He is MARIA'S cousin.
Answer 8: ¿Cuándo llegan los vecinos *de tí*?, ¿Cuándo llegan LOS VECINOS TUYOS?
Translation 8: When do *your* neighbors arrive? When do YOUR NEIGHBORS arrive?
Answer 9: María busca las llaves *de mi*. María busca MIS llaves.
Translation 9: Maria looks for the keys *to me*. Maria looks for MY keys.
Answer 10: ¿Son las hijas *de ustedes*?, ¿Son SUS hijas?
Translation 10: Are they *your* daughters? Are they YOUR daughters?
Answer 11: No conozco a la hermana *de él*. No conozco a la hermana DE ÉL.
Translation 11: I don't know *his* sister. I don't know HIS sister.
Answer 12: Es la culpa *de ti*.Es TU culpa.
Translation 12: It's *your* fault. It's YOUR fault.
Answer 13: Es la pintura *de nosotros*. Es NUESTRA pintura.
Translation 13: It's the painting *of us*. It's OUR painting.
Answer 14: Es la bolsa *de Carlota*.Es la bolsa DE CARLOTA.
Translation 14: It's *Carlota's* bag. It's CARLOTA's bag.
Answer 15: No puedo creer que los culpables son los amigo *de ti*. No puedo creer que los culpables son LOS AMIGOS TUYOS.
Translation 15: I can't believe that the culprits are *your* friends. I can't believe that the culprits are YOUR FRIENDS.
Answer 16: Es el éxito *de nosotros*. Es NUESTRO éxito.
Translation 16: It's the success *of us*. It is OUR success.
Explanation on the subject:
Possessive adjectives are words that indicate possession or ownership. In Spanish, possessive adjectives must agree in gender and number with the noun they modify. For example, "nuestras casas" (our houses) uses the feminine plural possessive adjective "nuestras" because "casas" is a feminine plural noun. The possessive adjective "mi" (my) changes to "mis" before a noun that begins with a vowel or a silent "h," as in "mis papeles" (my papers).