1. hers
These pencil is hers.
> This pencil is hers. / These pencils are hers.

2. mine
This gutar is mine.
> This guitar is mine.

3. yours
This scissors is yours.
> This pair of scissors is yours.

4. theirs
This cumputer is theirs.
> This computer is theirs.

5. ours
This piano in ours.
> This piano is ours.

Be mindful of the following:
* SPELLING
(x) gutar ~> guitar
(x) cumputer ~> computer

* SUBJECT VERB AGREEMENT
- This pencil is hers. (1 pencil) 
- These pencils are hers. (2 or more pencils)
Thank you for doing your homework, Adriano.