Someone signed a contract with the owner of the factory: he was paid 80 yuan a day if he worked, and if he didn’t work, he would have to pay 20 yuan a day in addition to not being paid. The implementation began on March 1. At the end of the month, he only received a salary of 1180 yuan. How many days did he work this month?
某人与厂家老板签订了一合同：工作一天得80元，若不工作的话除得不到工资外，一天还要上缴20元，3月1日开始执行．到月底结算时，他只领到工资1180元，本月他工作了多少天．
<gadget id="calculator">80 * 31</gadget>
<output>2_480</output>

<gadget id="calculator">2_480 - 1_180</gadget>
<output>1_300</output>

<gadget id="calculator">80 + 20</gadget>
<output>100</output>

<gadget id="calculator">1_300 / 100</gadget>
<output>13</output>

<gadget id="calculator">31 - 13</gadget>
<output>18</output>

<result>18</result>