In order to encourage residents to save water, our county charges tap water users according to the segmented billing method; if the monthly water consumption does not exceed 7m**3, it will be charged at 1 yuan per cubic meter; if it exceeds 7m**3 per month, The excess will be charged at 2 yuan per cubic meter. If a resident shared 15.6m**3 of water in May this year, how much should he pay for water?
我县城为鼓励居民节约用水，对自来水用户按分段计费方式收取水费；若每月用水不超过7m**3，则按每立方米1元收费；若每月超过7m**3，则超过部分按每立方米2元收费．如果某居民今年5月共用水15.6m**3，他应该交水费多少元？
<gadget id="calculator">1 * 7</gadget>
<output>7</output>

<gadget id="calculator">15.6 - 7</gadget>
<output>8.6</output>

<gadget id="calculator">2 * 8.6</gadget>
<output>17.2</output>

<gadget id="calculator">7 + 17.2</gadget>
<output>24.2</output>

<result>24.2</result>