The Bureau of Land and Resources has a piece of land of 0.2 square kilometers, and plans to build 4 factories on this land. Each factory covers an area of 4.5 hectares. How many hectares of land are left undeveloped?
国土局有一块0.2平方千米的地，准备在这块地上建4个工厂，每个工厂占地4.5公顷，还剩多少公顷土地没有得到开发利用？
<gadget id="calculator">0.2 * 100</gadget>
<output>20</output>

<gadget id="calculator">4.5 * 4</gadget>
<output>18</output>

<gadget id="calculator">20 - 18</gadget>
<output>2</output>

<result>2</result>