The children are planting trees on the side of the road. First plant one tree, and then plant one tree every 3 meters. There are already 9 trees planted. How many meters are the distance between the first tree and the ninth tree?
小朋友们在路的一边植树，先植一棵树，以后每隔3米植一棵，已经植了9棵，问第一棵和第九棵树相距多少米？
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<result>24</result>