Plant a tree every 20 meters on the side of a road, and plant 10 trees including both ends of the road. How long is this road in meters?
在一段路的路边每隔20米栽一棵树，包括这段路两端在内栽10棵树，这段路长多少米？
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">20 * 9</gadget>
<output>180</output>

<result>180</result>