A certain city has regulations on water use for residents: if each household uses no more than 10 tons of water per month, it will be charged at n yuan per ton; if the water consumption exceeds 10 tons, the excess part will be charged double. What is the actual water consumption of residents in January?
某市对居民用水规定：每户每月用水不超过10吨的，按每吨n元收费，用水量超过10吨的，超过部分加倍收费，某户居民1月份交水费16n元，那么该居民1月份实际用水量多少吨．
<gadget id="calculator">3 + 10</gadget>
<output>13</output>

<result>13</result>