There is a pasture where the grass grows evenly every day. 24 cows can be eaten in 6 days; 21 cows can be eaten in 8 days. To make the grass never run out, how many cows should be put at most.
有一片牧场，草每天均匀地长．24头牛6天可吃完；21头牛8天可吃完．要使草永远吃不完，至多放多少头牛．
<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 / 1</gadget>
<output>12</output>

<result>12</result>