In order to encourage water conservation, a certain city stipulates that the monthly water consumption of each household is less than 20 tons, and the price of water per ton is 1.5 yuan; for the part exceeding 20 tons, the price of water per ton is 2.1 yuan. Mingming’s family paid 46.8 yuan for water last month. How many tons of water does Mingming’s family share?
为鼓励节约用水，某城市规定每户每月用水量在20吨以内，每吨水价1.5元；超过20吨的部分，每吨水价2.1元．明明家上月缴水费46.8元，明明家共用水多少吨？
<gadget id="calculator">1.5 * 20</gadget>
<output>30</output>

<gadget id="calculator">46.8 - 30</gadget>
<output>16.8</output>

<gadget id="calculator">16.8 / 2.1</gadget>
<output>8</output>

<gadget id="calculator">8 + 20</gadget>
<output>28</output>

<result>28</result>