The surface area of the earth is about 510 million square kilometers, of which about (7/10) is ocean, and the rest is land. How many square kilometers is the land area of the earth?
地球的表面积大约是51000万平方千米，其中约(7/10)是海洋，其余的是陆地．地球上的陆地面积大约是多少万方千米？
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">51_000 * (3/10)</gadget>
<output>15_300</output>

<result>15_300</result>