This is the 740th most frequent Serbian word.
првој
The Serbian word "првој" is the dative or locative singular form of the feminine adjective meaning "first."
In this sentence, 'првој' is the dative feminine singular form of 'први', meaning 'first', indicating to whom the letter was sent.
Послао сам писмо првој ученици на списку.
I sent a letter to the first student on the list.
Here, 'првој' is the locative feminine singular form of 'први', describing the 'box' in which the photographs were found.
У првој кутији сам пронашао много старих фотографија.
In the first box, I found many old photographs.
'Првој' functions as the locative feminine singular form of 'први', specifying the desk's location where the girl is seated.