Questions & Answers about Doksan öğrenci odaya girdi.
After a number, Turkish normally uses the noun in the singular form.
So:
doksan öğrenci = ninety students
Even though English uses a plural noun after numbers, Turkish usually does not. Using öğrenciler after doksan would sound non-neutral in ordinary Turkish.
Oda means room.
The ending -(y)a / -(y)e is the dative case, often meaning to, into, toward.
So:
oda → odaya = to the room / into the room
The y appears because oda ends in a vowel. Turkish often inserts a buffer consonant between two vowels:
oda + a → odaya