This improvisation combines chords from a few different scales but is primarily in the key of Cm (the relative minor of Eb major). It features a descending bass line progression with some really nice harmony going on.
We start with a Cm chord which I am treating as chord I of C melodic Minor.
We then go to a B∆7#5 chord, which is chord III of Ab melodic minor.
The next two bars are back to our home key of Eb major
Bar 5 contains an Abm chord which we're treating as chord I of Ab melodic minor. Again, this is the melodic minor key built from the 4th degree of our home key, Eb major.
Bar 6 is back to Eb Major again.
Bar 7 contains an unusual addition to the key of an F#m6 chord which is functioning as chord I of F# melodic minor.
We finish back in the home key for the final two bars and the progression proceeds round and round.
Good luck here! Ask in the forums if you need help!