A person takes a boat down the Yangtze River and returns. The speed of the boat is 20km/h in still water and 4km/h in water. Every day the boat sails and stops for one day, there is only 29 days of gasoline on board. Then he goes down the river. How far away is the kilometer?
某人乘船沿着长江顺流而下并返回，船的静水速度为20km/h，水速4km/h，船每航行一天，停航一天，船上只有29天的汽油，那么他顺流而下最远多少千米？
<gadget id="calculator">20 + 4</gadget>
<output>24</output>

<gadget id="calculator">24 * 11.6</gadget>
<output>278.4</output>

<result>278.4</result>