4 sharps.
There are three flats in the key signature of E flat major
The key signature that has B flat, A flat, E flat and D flat is Concert A flat Major.
The key signature for F major has one flat (B flat) , while the key signature for F minor has four flats (B flat, E flat, A flat, and D flat).
The key signature of the F flat major key has six flats: B flat, E flat, A flat, D flat, G flat, and C flat.
A flat lowers the note by a semitone. As a key signature, a single flat indicates the key of F, meaning your B should be flat. Two flats are E and B, meaning the key is therefore B flat. B, E and A flat indicate the key of E flat ... and so on.
That is the signature for the key of Db. Or, it's relative minor, Bb minor.
B flat and E flat
The key signature of the C minor scale has three flats: B flat, E flat, and A flat.
B flat, E flat, A flat, D flat
That is C Minor
B flat, E flat, A flat, D flat, G flat, C flat, F flat. It's the opposite order to that of the sharps in a key signature.
The key signature of a piece written in F flat major has six flats: B flat, E flat, A flat, D flat, G flat, and C flat.