A passenger car and a truck depart from two stations A and B at the same time. They meet each other in 3 hours. After the encounter, the two cars continue to drive at their respective speeds. It is known that the bus travels for another 4 hours to reach Station B, and how many hours does the truck travel for to reach A stand?
一辆客车和一辆货车同时从甲乙两站相对开出，3小时相遇，相遇后两车都以各自速度继续行驶，已知客车又行了4小时到乙站，货车又行多少小时到甲站？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/7) * 3</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) / 3</gadget>
<output>4/21 = around 0.190476</output>

<gadget id="calculator">1 / (4/21)</gadget>
<output>21/4 = around 5.25</output>

<gadget id="calculator">(21/4) - 3</gadget>
<output>9/4 = around 2.25</output>

<result>9/4 = around 2.25</result>