Answer:
The correct answer is úsala.
Step-by-step explanation:
Laura: ¿Puedo usar tu computadora portátil?
Eva: Sí, claro, ¡úsala!
This means:
Laura: Can I use your laptop?
Eva: Yes, of course. Use it!
"Úsala" is imperative, but in this case it implies "of course, go ahead". "Úsela" is also grammatically correct but it is used in formal language. For instance, if Laura was Eva's boss or someone she doesn't know very well, she would answer using "úsela". "Usarla" is grammatically incorrect. And "úsenla" would be ok if it was directed to a group of people instead of Laura only, because it's plural.