The earth's surface area is about 510 million square kilometers, of which the land area is 149 million square kilometers. How many billion square kilometers is the ocean area?
地球表面积约5.1亿平方千米，其中陆地面积是1.49亿平方千米．海洋面积是多少亿平方千米？
<gadget id="calculator">5.1 - 1.49</gadget>
<output>3.61</output>

<result>3.61</result>