4.Simplificati, obtinand fractii ireductibile: 63/56•45

15/21=15/21simplificat la 3= 5/7
36/48=36/21 simplificat la 3= 12/7
63/56×45=63/2520 simplificat la 3=21/840 simplificat la 3=7/280 simplificat la 7=1/40
Succes!!