A passenger car drives from point A to point B, the ratio of the distance traveled in the first hour to the whole journey is 2:5. If you travel another 42 kilometers, you can reach the midpoint. How many kilometers are there between A and B?
一辆客车从A地开往B地，第一小时行的路程与全程的比是2：5．如果再行42千米，就可到达中点，A、B两地相距多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">42 / (1/10)</gadget>
<output>420</output>

<result>420</result>