The distance between A and B is a kilometer. A person rides a bicycle from A to B and travels 18 kilometers per hour. What is the average speed of the road in kilometers per hour.
甲、乙两地相距a千米，某人骑自行车从甲地去乙地，每小时行18千米，办完事后从地骑自行车返回甲地，每小时只行12千米，他往返这段路的平均速度是每小时多少千米．
<gadget id="calculator">1 * 2</gadget>
<output>2</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/18) + (1/12)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">2 / (5/36)</gadget>
<output>72/5 = around 14.4</output>

<result>72/5 = around 14.4</result>