Liu Ming rode a bicycle from home to school at 18 kilometers per hour. When she came back, the wind was headwind and she traveled 12 kilometers per hour. How many kilometers per hour did she travel on average on this journey?
刘明骑自行车从家到学校，每小时行18千米，回来时是逆风，每小时行12千米，她往返这段路平均每小时行多少千米．
<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>

<gadget id="calculator">1 * (72/5)</gadget>
<output>72/5 = around 14.4</output>

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