In order to save water, the water company stipulates that when the water used by each person does not exceed 3 tons per month, it will be charged at 2.6 yuan per ton, and the part exceeding 3 tons will be charged at 3.5 yuan per ton. According to this calculation, Beibei's family of 5 people paid a total of 43.9 yuan for water last month. How many tons of water did his family share last month?
为了节约用水，自来水公司规定：每人每月用水不超过3吨时，按每吨2.6元收费，超过3吨的部分按每吨3.5元收费．照这样计算，贝贝家5口人，上月共交水费43.9元，他家上月一共用水多少吨？
<gadget id="calculator">3 * 5 * 2.6</gadget>
<output>39</output>

<gadget id="calculator">43.9 - 39</gadget>
<output>4.9</output>

<gadget id="calculator">4.9 / 3.5</gadget>
<output>1.4</output>

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">1.4 + 15</gadget>
<output>16.4</output>

<result>16.4</result>