The Han River is the largest tributary of the Yangtze River. If the water velocity of the Yangtze River is 4 kilometers per hour, the water velocity of the Han River is 3 kilometers per hour. A ship sailed 115 kilometers downstream on the Han River to the Yangtze River in 5 hours, and traveled 128 kilometers upstream on the Yangtze River; how many hours did the ship travel in total?
汉江是长江最大的支流，若长江水流速度为每小时4千米，汉江水流速度为每小时3千米时．一艘轮船在汉江5小时顺水航行115千米到达长江，在长江逆水上行128千米；这艘轮船一共行了多少小时？
<gadget id="calculator">115 / 5</gadget>
<output>23</output>

<gadget id="calculator">23 - 3</gadget>
<output>20</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">128 / 16</gadget>
<output>8</output>

<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<result>13</result>