In the order of flats in key signatures, even if the melody skips the B-flat, the key would contain it, because there is no such key with only an E-flat.
The key with three flats (Bb, Eb, Ab) is the key of Eb.
Bb and Eb
Eb major/C minorAb major/F minorDb major/Bb minorGb major/Eb minor
No key signature could have only Eb and Gb, but some include those two e.g. Db Major, Gb Major, Bb minor and Eb minor.
Bb. B flat has two flats, the first two flats on the staff: Bb, and Eb. Also, the relative minor to Bb, G minor, also contains two flats in the key signature; Bb, and Eb. To find the relative minor to a major key, simply count down 2 and one half steps. ie: Bb, Ab, G, making the relative minor to Bb "G minor", which also has the same key signature.
That would be C minor, because often B natural is used instead of B flat.
It depends which Saxophone: soprano is in Bb, alto - Eb, tenor - Bb, baritone - Eb. they just sort of take it in turns with Bb and Eb!! (Also sopranino - Eb, soprillo - Bb and bass - Bb)
The key with three flats (Bb, Eb, Ab) is the key of Eb.
Eb Eb Eb Bb C C Bb G G F F Eb Bb Eb Eb Eb Bb C C Bb G G F F Eb Bb Bb Eb Eb Eb Bb Bb Eb Eb Eb Eb Eb Eb Eb Eb Eb Eb Eb Eb Bb C C Bb G G F F Eb Bb Bb C Bb D Eb
Bb and Eb
Bb Eb Bb Eb Bb Eb Bb Dm7 Gm7 Cm7 F7 Bb Eb Bb Eb Bb Eb Bb
Bb Bb C Bb Eb D Bb Bb C Bb F Eb Bb Bb Bb G Eb D C Ab Ab G Eb F Eb
Bb, Eb and Ab
It's not too bad, there's only three flats in the key signature; Bb, Eb, and Ab.
Bb Bb C Bb Eb D Bb Bb C Bb F Eb Bb Bb G F Eb D C Eb Eb D Bb C Bb
Bb, Bb, C, Bb, Eb, D Bb, Bb, C, Bb, F, Eb Bb, Bb, Bb(up an octave), G, Eb, D, C Ab, Ab, G, Eb, F, Eb
first row: Eb Eb Eb F Eb Eb Bb C Bb C ? Eb Eb Eb Eb Eb F Eb Eb Bb C Bb C ? Eb Eb I don't know the second row