Master Wang drove from A to B to deliver the goods. If he travels at a speed of 60 kilometers per hour back and forth, he can return to A on time. However, when he arrives at point B, he finds that his speed from point A to point B is only 55 kilometers per hour. If he wants to return to point A on time, how fast should he drive back?
王师傅驾车从甲地开乙地交货．如果他往返都以每小时60公里的速度行驶，正好可以按时返回甲地．可是，当到达乙地时、他发现他从甲地到乙地的速度只有每小时55公里，如果他想按时返回甲地，他应以多大的速度往回开？
<gadget id="calculator">2 / 60</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 55</gadget>
<output>1/55 = around 0.018182</output>

<gadget id="calculator">(1/30) - (1/55)</gadget>
<output>1/66 = around 0.015152</output>

<gadget id="calculator">1 / (1/66)</gadget>
<output>66</output>

<result>66</result>