There is a rectangular field with a length of 42 meters and a width of 18 meters. If one tree is planted every 9 square meters, how many trees can be planted on this land?
有一块长方形地，长42米，宽18米．如果每9平方米栽一棵树，这块地一共能栽多少棵树？
<gadget id="calculator">18 / 9</gadget>
<output>2</output>

<gadget id="calculator">42 * 2</gadget>
<output>84</output>

<result>84</result>