A rectangular piece of ground is 120 meters long and 30 meters wide. Trees are to be planted around and at its four corners. The distance between every two adjacent trees is equal. What is the minimum number of trees to be planted?
一块长方形地面，长120米，宽30米，要在它的四周和四角种树，每相邻两棵树之间的距离相等，最少要种多少棵数．
<gadget id="calculator">120 + 30</gadget>
<output>150</output>

<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">150 * (1/15)</gadget>
<output>10</output>

<result>10</result>