If the grass in a pasture can last 6 days for 24 cows, or 8 days for 21 cows, how many days can the grass in this pasture last for 16 cows?
一个牧场的草可供24头牛吃6天，或供21头牛吃8天，那么这个牧场的草可供16头牛吃多少天．
<gadget id="calculator">24 * 6</gadget>
<output>144</output>

<gadget id="calculator">21 * 8</gadget>
<output>168</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 * 6</gadget>
<output>72</output>

<gadget id="calculator">144 - 72</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>