A road is 90 meters long, and a tree is planted every 10 meters on both sides of it from the beginning, how many trees will be planted in total at the end?
一条马路长90米，在它的两边从头开始每隔10米栽一棵树，到最后一共要栽多少棵？
<gadget id="calculator">90 / 10</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>