Plant trees around a rectangular land with a length of 100 meters and a width of 80 meters. Plant trees every several meters. A total of 20 trees have been planted. Find the distance between each two trees.
在一块长100米，宽80米的长方形地的周围种树，每隔若干米种一棵，共种了20棵，求每两棵之间的距离．
<gadget id="calculator">100 + 80</gadget>
<output>180</output>

<gadget id="calculator">2 / 20</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">180 * (1/10)</gadget>
<output>18</output>

<result>18</result>