is most likely in the Key of F Major
Notes in F Major:
A, A#/Bb, C, D, E, F, G
Chords in F Major:
F, Gm, Am, Bb, C, Dm, Edim
This key can also be known as D minor.
When it's used as a minor key, the minor key note is stressed more than the major key note. The same notes and same chords still apply.