Water fee adjustment announcement: If the monthly water consumption does not exceed 15 tons, it will be charged at 1.20 yuan per ton; if it exceeds 15 tons, the excess part will be charged at 5.00 yuan per ton. The water fee for Dongdong’s family this month is 39 yuan. How many tons of water did Dongdong’s family use this month?
水费调整公告：若每月用水不超过15吨，则按每吨1.20元收费，若超过15吨，则超出的部分按每吨5.00元收费．冬冬家这个月的水费是39元，冬冬家这个月用了多少吨水？
<gadget id="calculator">11 / 5</gadget>
<output>11/5 = around 2.2</output>

<gadget id="calculator">15 + (11/5)</gadget>
<output>86/5 = around 17.2</output>

<result>86/5 = around 17.2</result>