Simplify the following text for a Grade 7 native English-speaking person.
Original: Put another way : for key signatures with sharps , the first sharp is placed on F line with subsequent sharps on C , G , D , A , E and B ; for key signatures with flats , the first flat is placed on B with subsequent flats on E , A , D , G , C and F. There are thus 15 conventional key signatures , with up to seven sharps or flats and including the empty signature of C major ( A minor ) .
Simplified: There are fifteen possible key signatures : up to seven sharps , up to seven flats , or no sharps or flats . The reason why there are fifteen and not twelve is because three of them have two possible names : F sharp major ( 6 sharps ) can also be called G flat , C sharp is D flat and B is C flat .