The Xingguang community carried out water saving activities. Grandma Wang’s family saved 21.6 yuan in water bills in the first half of the year, and Grandma Zhang’s family saved a total of 16.2 yuan in water bills in the first quarter. Which family saves more water bills per month on average? How much?
星光小区开展节约用水活动，王奶奶家上半年节约水费21.6元，张奶奶家第一季度共节约水费16.2元，谁家平均每月节约的水费多？多多少？
<gadget id="calculator">16.2 / 3</gadget>
<output>5.4</output>

<gadget id="calculator">21.6 / 6</gadget>
<output>3.6</output>

<gadget id="calculator">5.4 - 3.6</gadget>
<output>1.8</output>

<result>1.8</result>