There is a pasture where pasture grows at a constant rate every day and can feed 9 cows for 12 days and 8 cows for 16 days. Now there are only 4 cows to eat, and a few more cows have been added since the 7th day, and the grass used is eaten up in 6 days, how many cows have been added.
有一牧场，牧草每天匀速生长，可供9头牛吃12天；可供8头牛吃16天．现在开始只有4头牛吃，从第7天开始又增加了若干头牛，再用6天吃光所用的草，问增加了多少头牛．
<gadget id="calculator">12 * 9</gadget>
<output>108</output>

<gadget id="calculator">16 * 8</gadget>
<output>128</output>

<gadget id="calculator">128 - 108</gadget>
<output>20</output>

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

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 12</gadget>
<output>60</output>

<gadget id="calculator">108 - 60</gadget>
<output>48</output>

<gadget id="calculator">5 * 6</gadget>
<output>30</output>

<gadget id="calculator">4 * 6</gadget>
<output>24</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">48 + 6</gadget>
<output>54</output>

<gadget id="calculator">54 + 30</gadget>
<output>84</output>

<gadget id="calculator">84 / 6</gadget>
<output>14</output>

<gadget id="calculator">14 - 4</gadget>
<output>10</output>

<result>10</result>