From A to B, the uphill road accounts for (2/7), the flat land accounts for (4/7), and the rest is downhill. A car goes back and forth between A and B once, and travels a total of 42 kilometers downhill. How many miles is the distance between A and B?
从甲地到乙地，上坡路占全程的(2/7)，平地占(4/7)，其余是下坡路．一辆汽车在甲、乙两地间往返一次，共行下坡路42千米．甲乙两地间的路程是多少千米．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

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

<gadget id="calculator">(2/7) + (1/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">42 / (3/7)</gadget>
<output>98</output>

<result>98</result>