Question

Julio: No, hombre. Pero hay muchas __________________ en la biblioteca. Tienen la red y todo. Yo mandé un e-mail a muchos amigos y recibí la de Iris-Teresa. Es muy fácil.

Answer 1

It could be "libros" because books are in the library.

Answer 2

It can't be what Tovelofan said, because "muchas" is in femenine, while "libros" is masculine.

In the sentence it talks about going to the library and sending emails. The only thing you can send emails with are computers.
Therefore, you have two options:

- Ordenadores. This is the Spain's Spanish word for computers. This word is masculine

- Computadoras. This is the Latin American's Spanish word for computers. This word is femenine.

As I said, "muchas" is femenine, and therefore, the noun has to be femenine, too, so the only option is "computadoras"