After switching to water-saving faucets, Aunt Zhang's family saved 72 yuan in water bills in the first half of last year, and Aunt Li's family saved a total of 45.6 yuan in water bills in the fourth quarter of last year. Which one saves more water bills per month on average? How much more?
改用节水龙头后，张大妈家去年上半年节约水费72元，李大妈家去年第四季度共节约水费45.6元．哪家平均每月节约的水费多一些？多多少元？
<gadget id="calculator">45.6 / 3</gadget>
<output>15.2</output>

<gadget id="calculator">72 / 6</gadget>
<output>12</output>

<gadget id="calculator">15.2 - 12</gadget>
<output>3.2</output>

<result>3.2</result>