A rectangular piece of land is 60 meters long and 30 meters wide. Trees are to be planted on the four sides with a distance of 6 meters. There is one tree at each of the four corners. How many trees are planted in total?
一块长方形地，长为60米，宽为30米，要在四边上植树，株距6米，四个角上各有一棵，共植树多少棵．
<gadget id="calculator">60 + 30</gadget>
<output>90</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">180 / 6</gadget>
<output>30</output>

<result>30</result>