Answer:
las mochilas, las sillas, los escritorios, los libros, los cuadernos, los lapices
Explanation
- La will become las when going from singular to plural
- El will become los when going from singular to plural
- In most cases, you can just add an s to the end of the noun and it will become plural. However, for el lápiz, you can't add an s to the end of the noun, so the spelling changes.