It took Xiao Kai 18 minutes to go to her grandmother's house by car, but she changed to walk when she went there, and took a car when she came back. It took 47 minutes. How many minutes did it take him to walk?
小凯到外婆家，如果来去都乘车要用的时间是18分钟，后来改为去时步行，回来乘车，一共用了47分钟．他去时步行用了多少分钟？
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">47 - 9</gadget>
<output>38</output>

<result>38</result>