Halo teman! The Indonesian "menghilang" / "hilang", in this exercise, could be translated as "to be gone", "to disappear", "to vanish", always as an intransitive verb. So, it is applied to the same subject, to "oneself".
The transitive verb would be "menghilangkan".
Dengan mudah dia MENGHILANG di keramaian pasar malam itu. => She easily DISAPPEARED in the bustle of that night market. (intransitive)
Si Tarjo yang MENGHILANGKAN kunci mobil ayah. => Tarjo was the one who LOST the keys to father's car. (transitive)
I hope it helps.
Selamat belajar! :)