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