12x=(5+4+3)×4
12x=48
x=4
Suppose his family used x tons of water this month.
4× 1.8+(x-4)×3 = 1 1.7
(x-4)×3=4.5
x-4= 1.5
x=5.5
We assume that the speed of the train from Nanjing is X kilometers per hour.
( 154+x)×2=568
154+x=284
x= 130