39. The function relationship between the monthly water fee $y$ (yuan) and the water consumption $x$ (tons) for a user is shown in the figure. Then, the charging standard for monthly water consumption of 4 tons or less (including 4 tons) is $\qquad$ yuan/ton, and the charging standard for the part exceeding 4 tons is $\qquad$ yuan/ton. If the user pays a water fee of 12.8 yuan in a certain month, then he used $\qquad$ tons of water that month.
Answer: $1.2 ; 1.6 ; 9$