Assuming that the original sales price is X yuan per kWh,

The unified electricity price is (x+0.03) yuan per kWh,

The electricity price in valley section is (x-0.25) yuan per kWh.

Equation: 40(x+0.03)+60(x-0.25)=42.73,

Solution: x = 0.5653 (yuan)

The flat electricity price paid by Xiao Ming's family this month is:

40(x+0.03) = 23.8 12 (yuan)

The valley electricity price paid by Xiao Ming's family this month is:

60 (x-0.25) =18.918 (yuan)

2、

If the time-of-use electricity price is not used for settlement, Xiaoming's family will pay more in May:

(40+60)x-42.73 = 13.8 (yuan)