B7/A Piano Chord
B7/A is a B Dominant 7th chord played over a A bass note. Because A is the ♭7th of B Dominant 7th, B7/A is simply B Dominant 7th in 3rd inversion — the same notes, with the ♭7th moved to the bottom.
The dark key is the bass note (A); the coloured keys are the B Dominant 7th chord tones.
Notes in B7/A
Low to high: A (bass) , then B – D♯ – F♯ – A.
How to play B7/A
Play the bass note A low in your left hand, and the B Dominant 7th chord (B – D♯ – F♯ – A) in your right. Because it's an inversion, the bass is already one of the chord tones — you're just voicing B Dominant 7th with its ♭7th on the bottom.