Here are the answers filled in with the possessive form:

1. Do you see **my** hat? (I)
2. Can you give me **your** ruler? (you)
3. This is **our** classroom. (we)
4. James doesn’t know **his** phone numbers. (they)
5. I don’t like **his** carpet. (he)
6. Here is **her** dishwasher. (she)
7. The cat is finding **its** food. (it)
8. This is **Peter's** book. (Peter)
9. This is **the children's** room is upstairs. (children)
10. **John's** sister is twelve years old. (John)
11. **Susan and Steve's** school is old. (Susan and Steve)
12. **The men's** shoes are on the second floor. (Men)
13. My **parents'** car is not expensive. (parents)
14. This is **the boy's** bike. (the boy)
15. These are **the girls'** pencils. (the girls)
16. Her **cousin's** hat is on the table. (cousin)
17. There is a butterfly in front of my **sister's** computer. (sister)
18. Where is **Sarah's** house? (Sarah)