prima cutie /--------------------/
a doua cutie /--------------------/------/
total /--------------------/------------------/-----/ 24 masinute
24 - 4 = 20
20 : 2 = 10 masinute in prima cutie
10 + 4 = 14 masinute in a doua cutie
verificare: 10 + 14 = 24 masinute