Actually, you should learn what feels right in the language you're learning. I have learnt French to a reasonable level by feeling how each phrase goes, rather than by thinking about it which would make me speak very unnaturally with big pauses!
It's actually in its neuter form! Adjectives with -IG ending do not accept any final T.
en/ei vanskelig bok [= a difficult book]
et vanskelig arbeid [= a difficult work]
vanskelige bøker [= difficult books]