In order to save water, on January 1, 2016, the city implemented new charging standards, as follows, each household’s monthly water consumption does not exceed 20 cubic meters per cubic meter, 2.1 yuan per cubic meter, and the excess is 3.5 yuan per cubic meter. Since Xiao Li's family did not take water-saving measures, they paid a water fee of 56 yuan in May. How much is the actual water used?
为了节约用水，2016年1月1日，我市收费实施新标准，具体如下，每户每月用水量不超过20方的每方2.1元，超过部分则每方3.5元．由于小李家没有采取节水措施，5月分交了水费56元，求实际用水多少方？
<gadget id="calculator">2.1 * 20</gadget>
<output>42</output>

<gadget id="calculator">56 - 42</gadget>
<output>14</output>

<gadget id="calculator">14 / 3.5</gadget>
<output>4</output>

<gadget id="calculator">4 + 20</gadget>
<output>24</output>

<result>24</result>