A car drives from place A to place B. It travels 40% of the whole journey in 3 hours. At this time, it is 42km away from half of the journey. How many kilometers per hour does this car drive on average?
一辆汽车从甲地开往乙地，3小时行了全程的40%，这时离全程的一半还有42km，这辆汽车平均每小时行多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 / 100</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">(2/5) / 3</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">420 * (2/15)</gadget>
<output>56</output>

<result>56</result>