Why not "Is this useful?"
It's an accepted answer, it should have worked.
why here plural (przydatne) and singular, (it is)? together
as usually the hint is misleading.
As with all adjectives:
nom. sing. neuter = nom. plural not masc pers= acc. sing neuter=acc. plural not masc pers
here it is nominative singular neuter, as it describes "to"
Is it handy?
Makes sense, added.