Watch the 1 5 1 Structures online guitar lesson by Brad Carlton from Guitar Lab: Open String Universe
This chord is A root 5th root structure rooted off the 9th fret of the 5th string. The 2nd string open is a B which is the 4(11) in the key of F#. The 1st string open is an E which is the b7 in the key of F#. The total formula of this voicing is 1 4 5 b7 therefore it is an F#7sus4. The formula 1 4 5 b7 is a subset of the following scales: dorian, phrygian, mixolydian, aeolian, phrygian dominant, mixolydian b6. The included chart shows this chord/scale relationship for the 7sus4 harmony.