It is estimated that the resources on the earth can be used for 90 years for 11 billion people, or 210 years for 9 billion people. Assuming that the growth rate of newly generated resources on the earth is constant, then in order to enable human beings to continue to multiply, the earth can support up to how many billions of people.
据测算，地球上的资源可供110亿人生活90年，或可供90亿人生活210年．假设地球上新生成的资源的增长速度是一定的，那么为使人类能够不断繁衍，地球最多能养活多少亿人．
<gadget id="calculator">210 * 90</gadget>
<output>18_900</output>

<gadget id="calculator">110 * 90</gadget>
<output>9_900</output>

<gadget id="calculator">18_900 - 9_900</gadget>
<output>9_000</output>

<gadget id="calculator">210 - 90</gadget>
<output>120</output>

<gadget id="calculator">9_000 / 120</gadget>
<output>75</output>

<result>75</result>