The ocean area on the earth's surface is about 360 million square kilometers, which is 210 million square kilometers larger than the land area. How many billion square kilometers is the land area? (column equation solution)
地球表面的海洋面积大约是3.6亿平方千米，比陆地面积多2.1亿平方千米．陆地面积大约是多少亿平方千米？(列方程解答)
<gadget id="calculator">3.6 - 2.1</gadget>
<output>1.5</output>

<result>1.5</result>