Xiaohong and her mother were walking on the side of the road. There was a row of trees evenly planted on the side of the road. It took them 7 minutes to walk from the first tree to the 22nd tree. Then they walked forward a few trees and then turned back. , It took 28 minutes for them to return to the fifth tree, so Xiaohong started walking back when she walked with her mother to the first tree.
小红跟妈妈在马路边散步，路边均匀地栽着一行树，她们从第1棵树走到第22棵树用了7分钟，然后她们又往前走了几棵树后就往回走，当她们回到第5棵树时一共用了28分钟，那么小红是跟妈妈散步走到第多少棵树时开始往回走的．
<gadget id="calculator">28 - 7</gadget>
<output>21</output>

<gadget id="calculator">22 - 1</gadget>
<output>21</output>

<gadget id="calculator">7 / 21</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">21 / (1/3)</gadget>
<output>63</output>

<gadget id="calculator">22 - 5</gadget>
<output>17</output>

<gadget id="calculator">63 - 17</gadget>
<output>46</output>

<gadget id="calculator">46 / 2</gadget>
<output>23</output>

<gadget id="calculator">22 + 23</gadget>
<output>45</output>

<result>45</result>