18 carti...50 file
...80 file
total file = 1050
18x50=900(presupunem ca toate cartile au 50 file)
1050-900= 150
80 file - 50 file = 30 file ( diferenta de file dintre tipurile de carti)
150:30=5 =>5 carti cu 80 de file
5x80=400
1050-400=750
750:50=13 carti cu 50 file
