The road in the center of the school is 200 meters long, and a tree is planted every 10 meters on both sides of the road. How many trees are planted in total?
学校中心路长200米，在路两侧从头到尾每隔10米栽一棵树，共栽多少棵树？
<gadget id="calculator">200 / 10</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>