An express bus drives from place A to place B at 8:00 in the morning, and just completed the whole journey (2/5) at 2:00 in the afternoon. At this time, the car is still 42 kilometers away from half of the journey. How many miles per hour does the car travel on average?
一辆快客上午8：00从甲地开往乙地，到下午2：00正好走完了全程的(2/5)，这时汽车离全程的一半还差42千米．问这辆汽车平均每小时行驶多少千米？
<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>

<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">(2/5) / 6</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">420 * (1/15)</gadget>
<output>28</output>

<result>28</result>