a few ways to tell a minor key apart from a major is when you look at the score go directly to the last bar. more often than not it will end on the one. in this music it’s an A so there’s your first clue.
the other thing we can do is check for four chords and five chords throughout because every song will have these chords.
so in the key of A major we will see some D chords and some E chords.
if the song was in F# minor we would see some C# chords and some D# chords
now with this information take a long look at the score and you’ll see what I mean.