The distance between A and B is 420 kilometers. A passenger car and a truck depart from the two places at the same time and meet each other after 7 hours. Given that the speed ratio of passenger cars and trucks is 8:7, how many hours will it take for the truck to complete the journey?
甲、乙两地相距420千米，客车和货车同时分别从两地相对开出，经过7小时相遇．已知客车和货车的速度比为8：7，求货车行完全程要用几小时？
<gadget id="calculator">420 / 7</gadget>
<output>60</output>

<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<gadget id="calculator">7 / 15</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">60 * (7/15)</gadget>
<output>28</output>

<gadget id="calculator">420 / 28</gadget>
<output>15</output>

<result>15</result>