A and B travel from two places 30 kilometers apart to the starting point of each other at a speed of 6 kilometers per hour and 4 kilometers per hour respectively. When the distance between the two is 10 kilometers. How many hours did they walk?
甲、乙两人分别以每小时6千米、每小时4千米的速度从相距30千米的两地向对方出发地前进，当两人的距离为10千米时．他们走了多少小时？
<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">4 + 6</gadget>
<output>10</output>

<gadget id="calculator">40 / 10</gadget>
<output>4</output>

<result>4</result>