24 cows can eat a piece of pasture in 6 days, and 21 cows can eat up this piece of pasture in 8 days. If the growth of grass is equal every day, in order to prevent desertification of the grassland, how many cows can eat the pasture at most? Only then can this piece of grass never be eaten up.
24头牛6天可以将一片牧草吃完，21头牛8天可以将这片牧草吃完，如果每天草的增长量是相等的，为了防止草地沙化，最多放多少头牛吃这片牧草，才能使这片草永远吃不完．
<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>

<result>12</result>