A 6/C
The A 6 chord consists of the A (Perfect unison), C# (Major third), E (Perfect fifth) and F# (Major sixth) notes, with C as the bass note.

How to play the A 6/C chord
- Play C as the lowest bass note in the left hand
- Find A (Root) on the piano keyboard
- Add C# (Major third) — 4 semitones above A
- Add E (Perfect fifth) — 7 semitones above A
- Add F# (Major sixth) — 9 semitones above A
- Press all 5 notes simultaneously to sound the A 6/C chord