It takes 18 minutes for Xiaohua to go to her grandma's house by car. When she goes there, she walks. When she comes back, she takes a car. It takes 45 minutes to go back and forth. How many minutes does it take to walk?
小华去奶奶家，路上乘车要18分钟，她去时步行，回来乘车，来回路上用了45分钟，步行用了多少分钟？
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">45 - 9</gadget>
<output>36</output>

<result>36</result>