Mingming went to grandma’s house by bicycle, drove 12 kilometers per hour, and arrived at the destination in 3 hours. When returning, he encountered strong winds and only traveled 9 kilometers per hour. How long did it take Mingming to return?
明明骑车去外婆家，每小时行驶12千米，3小时到达目的地，返回时遇上大风，每小时只行驶9千米，明明返回用了多长时间？
<gadget id="calculator">3 / 9</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">12 * (1/3)</gadget>
<output>4</output>

<result>4</result>