It takes 10 hours and 15 hours for A and B to drive from A to B respectively. If B starts 3 hours first, how many hours can A catch up with B?
甲、乙两车从A地开往B地分别需要用10个小时和15个小时，若乙车先出发3小时，则甲车出发多少小时后能追上乙车．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 3</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) - (1/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/5) / (1/30)</gadget>
<output>6</output>

<result>6</result>