Xiaoming’s family used an average of 18 tons of water per month last year. If it is calculated at 3 yuan per ton of water, how much water bills did Xiaoming’s family pay last year?
小明家去年平均每月用水18吨，如果按每吨水3元计算，小明家去年一共应付水费多少元？
<gadget id="calculator">3 * 18 * 12</gadget>
<output>648</output>

<result>648</result>