Fast, medium and slow cars travel from A to B, and a person on a motorcycle travels from B to A. The person takes 6, 10, and 15 minutes to meet the three cars respectively. The fast car is 80 kilometers per hour, and the medium car is 40 kilometers per hour. Hourly, ask for the slow speed?
快、中、慢三车从甲到乙，有一骑摩托车的人从乙到甲，该人分别用6、10、15分钟与三车相遇，快车80千米每小时，中车40千米每小时，求慢车速度？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 80</gadget>
<output>8</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 40</gadget>
<output>20/3 = around 6.666667</output>

<gadget id="calculator">8 - (20/3)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(1/6) - (1/10)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(4/3) / (1/15)</gadget>
<output>20</output>

<result>20</result>