How can you measure 9liter using 2 gallons of 12 liters and 5 liters?
8 Steps
Steps <------> 2L Gallon <-------> 5L Gallon
1<--------------->12<--------------->0
2<--------------->07<--------------->5
3<--------------->07<--------------->0
4<--------------->02<--------------->5
5<--------------->02<--------------->0
6<--------------->00<--------------->2
7<--------------->12<--------------->2
8<--------------->09<--------------->5
