The distance between AB and AB is 900 kilometers. A passenger car and a freight train travel towards each other from AB at the same time. They meet each other in 6 hours. After the meeting, the passenger car travels for another 4 hours to reach B. How many hours will the truck have to drive to reach point A at this time?
AB两地相距900千米，一列客车和一列货车同时从AB两地相向而行，6小时相遇，相遇后客车又行了4小时到达B地．这时货车还要行驶多少小时才能到达A地？
<gadget id="calculator">900 / 6</gadget>
<output>150</output>

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

<gadget id="calculator">900 / 10</gadget>
<output>90</output>

<gadget id="calculator">150 - 90</gadget>
<output>60</output>

<gadget id="calculator">900 / 60</gadget>
<output>15</output>

<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<result>9</result>