There can be a total of seven flats (or sharps) in a key signature.
Cb major has all 7 flats
six
Two flats, B flat and E flat
There are no flats in D major, but there are 2 sharps. C sharp and F sharp.
The key of A-flat major contains four flats: B, E, A, and D.
Just one
3
six
Three
four
The answer depends on the size of the cube.