Dad rides a motorcycle to work, travels 50 kilometers per hour, and arrives at the unit in (3/10) hours. If he rides a bicycle instead, it will take (5/7) hours to reach the unit along the original road. How much does Dad ride a bicycle per hour? km?
爸爸骑摩托车去上班，每小时行50千米，(3/10)小时到达单位，如果他改骑自行车，则沿原路到达单位需(5/7)小时，爸爸骑自行车每小时行多少千米？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(3/10) / (5/7)</gadget>
<output>21/50 = around 0.42</output>

<gadget id="calculator">50 * (21/50)</gadget>
<output>21</output>

<result>21</result>