There is a piece of grass that grows evenly every day. If 24 sheep eat it, it can be eaten in 6 days; if 21 sheep eat it, it can be eaten in 8 days. If 16 sheep eat grass, how many days can they finish eating?
有一片草地上的草每天都均匀地生长，如果24只羊吃，则6天可吃完；如果21只羊吃，则8天可以吃完．如果16只羊吃草，则可多少天吃完．
<gadget id="calculator">21 * 8</gadget>
<output>168</output>

<gadget id="calculator">24 * 6</gadget>
<output>144</output>

<gadget id="calculator">168 - 144</gadget>
<output>24</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<gadget id="calculator">12 * 8</gadget>
<output>96</output>

<gadget id="calculator">168 - 96</gadget>
<output>72</output>

<gadget id="calculator">16 - 12</gadget>
<output>4</output>

<gadget id="calculator">72 / 4</gadget>
<output>18</output>

<result>18</result>