The secondary water consumption is 7 tons (25- 18), and the cost1.8× (25-18) =12.6 yuan.

Tertiary water consumption (extra money): 51-34.2-12.6 =16.8 (yuan)

Tertiary water consumption: 16.8/2.4=7 (ton)

The water consumption of Wang Wenjia in May is 18+7+7=32 (tons).

A: The water consumption of Wang Wen's family in May was 32 tons.