A car travels 90 kilometers per hour. Uncle Ding travels 1/3 of the distance traveled by a car per hour on a motorcycle. Uncle Zheng rides a bicycle 15 kilometers slower than Uncle Ding rides a motorcycle. rice. How many kilometers per hour does Uncle Zheng ride a bicycle?
一辆小轿车每小时行驶90千米，丁叔叔骑摩托车每小时所行距离是小轿车每小时行驶距离的(1/3)，郑叔叔骑自行车比丁叔叔骑摩托车每小时慢15千米．郑叔叔骑自行车每小时行多少千米？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">90 * (1/3)</gadget>
<output>30</output>

<gadget id="calculator">30 - 15</gadget>
<output>15</output>

<result>15</result>