A ship sails from port A to port B, which is 713 kilometers away, and it takes 23 hours to reach it along the current, and 31 hours to reach it against the current when it returns. What is the speed of the ship in kilometers in still water?
一只船从甲港开往相距713千米的乙港，去时顺水23小时到达，返回时逆水则需要31个小时到达，船在静水中的速度是多少千米．
<gadget id="calculator">713 / 23</gadget>
<output>31</output>

<gadget id="calculator">713 / 31</gadget>
<output>23</output>

<gadget id="calculator">31 - 23</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">31 - 4</gadget>
<output>27</output>

<result>27</result>