Xiaoming's family used to pay an average water bill of 23 yuan per month. After installing the water saving valve, they paid 102 yuan for water in the first six months of this year. How much is the average monthly water saving?
小明家以前平均每月交水费23元，装上节水阀后，今年前6个月交水费102元，平均每月节约水费多少元？
<gadget id="calculator">102 / 6</gadget>
<output>17</output>

<gadget id="calculator">23 - 17</gadget>
<output>6</output>

<result>6</result>