RAM has nailed this one for you
To add a little more info...
As RAM has said it depends on the context in which you are naming that "A" note
If it is in relation to the degree of the Major scale (in this case C Major) the A note is the sixth note (or degree) of the major scale
The snappier name for the sixth note is called the "submediant" as it is in the middle of the "upper tonic" (the C at the end of the scale) and the "subdominant" (the fourth note of the scale, which in C Major is the F)
However, in the context of the A Minor chord the A would simply be the root note
Finally, as RAM has pointed out, if the key (tonal centre) is A minor (implied by the choice and order of chords along with how the melody is constructed and resolved) then the A note becomes the tonic note of A Minor