The charging standard of a taxi in a certain city is as follows: within 2.5km (including 2.5km), the fee is 6 yuan; for more than 2.5km, the fee is 1.6 yuan per kilometer (less than 1km is charged as 1km). Uncle Wang took a taxi from home to the Science and Technology Museum, and paid a total of 15.6 yuan for the taxi. How many kilometers is the longest distance from Uncle Wang's house to the Science and Technology Museum?
某市出租车的收费标准如下：2.5km以内(含2.5km)收费6元，超过2.5km，每千米收费1.6元(不足1km按1km计费)．王叔叔从家打车去科技馆，共付车费15.6元．王叔叔家到科技馆的路程最远是多少千米？
<gadget id="calculator">15.6 - 6</gadget>
<output>9.6</output>

<gadget id="calculator">9.6 / 1.6</gadget>
<output>6</output>

<gadget id="calculator">6 + 2.5</gadget>
<output>8.5</output>

<result>8.5</result>