We have the adjective nou meaning new. All of it's forms, depending on gener and number, are:
- câine nou (new dog - masculine singular)
- pisică nouă (new cat - feminine singular)
- câini noi (new bears - masculine plural)
- pisici noi (new cats - feminine plural)
The number nine is nouă.
In this particular scenario it is obviously the number nouă because nouă (as new) would've been noi here.
Usually we don't have issues figuring it out because we say:
- Eu am nouă pisici (I have nine cats)
- Eu am o pisică nouă (I have a new cat)
- Pisica este nouă (the cat is new)
- Pisicile sunt noi (the cats are new)
- Pisicile sunt nouă (the cats are nine)