The distance traveled by car A to the county seat is three times the distance traveled by car B to the county seat. Car A travels 60 kilometers per hour, and car B travels 40 kilometers per hour. Cars A and B set off for the county seat at the same time. When car B arrives at the county seat, car A is still 15 kilometers away from the county seat. How many kilometers is the distance from car A to the county seat?
甲车到县城的路程是乙车到县城路程的3倍．甲车每小时行60千米，乙车每小时行40千米．甲乙两车同时出发去县城，当乙车到县城时，甲车距县城还有15千米．甲车到县城的路程有多少千米？
<gadget id="calculator">15 / 60</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3 / 60</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/20) - (1/40)</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/4) / (1/40)</gadget>
<output>10</output>

<gadget id="calculator">3 * 10</gadget>
<output>30</output>

<result>30</result>