rectangular piece of land is 42 meters long and 15 meters wide. If one tree is planted every 3 square meters, how many trees can be planted in total?
一块长方形的土地，长是42米，宽是15米，如果每3平方米种一棵树，一共可以种多少棵树？
<gadget id="calculator">42 * 15</gadget>
<output>630</output>

<gadget id="calculator">630 / 3</gadget>
<output>210</output>

<result>210</result>