3 robinete .............. 4ore.............10800 l
1 robinet...................4 ore...........x = 10800/3= 3600 l
1robinet....................1 ora...................................y = 3600/4 = 900 l
5 obinete...................1 ora...............z = 900·5 = 4500 l
5 robinete................3 ore...............t = 4500·3 = 13500 l