Xiaohong rides a bicycle from A to B, traveling an average of 12 kilometers per hour, and arrives in 4.2 hours. It only takes 3.2 hours to go back. How many kilometers per hour does the average travel on the way back?
小红骑自行车从甲地到乙地，平均每小时行12千米，4.2小时到达，回去时只用了3.2小时，回去时平均每小时行多少千米？
<gadget id="calculator">4.2 / 3.2</gadget>
<output>1.3125</output>

<gadget id="calculator">12 * 1.3125</gadget>
<output>15.75</output>

<result>15.75</result>