Uncle Wang rode a bicycle from home to the county seat. He rode 15 kilometers per hour for 4 hours. When he came back, he didn’t have enough energy and took an extra hour. How many kilometers per hour did he ride when he came back?
王叔叔从家骑自行车到县城，去时每小时骑15千米，用了4小时，回来时因体力不够，多用了一小时，回来时每小时骑多少千米？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 * (4/5)</gadget>
<output>12</output>

<result>12</result>