Uncle Li is walking on the side of the road, and a row of trees is evenly planted on the side of the road. It takes 7 minutes for Uncle Li to walk from the first tree to the 15th tree. Uncle Li walks forward a few more trees and then turns back. When he returned to the fifth tree, it took 30 minutes. When Uncle Li walked to the first tree, he started to walk back to the first tree.
李大爷在马路边散步，路边均匀地栽着一行树，李大爷从第1棵树走到第15棵树共用了7分钟，李大爷又向前走了几棵树后就往回走，当他回到第5棵树时共用了30分钟，李大爷步行到第几棵树时就开始往回走第多少棵
<gadget id="calculator">30 - 7</gadget>
<output>23</output>

<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">7 / 14</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">23 / (1/2)</gadget>
<output>46</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<gadget id="calculator">46 - 10</gadget>
<output>36</output>

<gadget id="calculator">36 / 2</gadget>
<output>18</output>

<gadget id="calculator">15 + 18</gadget>
<output>33</output>

<result>33</result>