There is a piece of grass that grows at the same rate every day. It is known that this piece of grass can feed 15 cows for 20 days, or 76 sheep for 12 days. If a cow eats as much grass as 4 sheep, how many days can 8 cows eat with 64 sheep?
有一片青草，每天生长速度相同，已知这片青草可供15头牛吃20天，或者供76只羊吃12天．如果一头牛的吃草量相当于4只羊的吃草量，那么8头牛与64只羊一起吃，可以吃多少天？
<gadget id="calculator">15 * 4 * 20</gadget>
<output>1_200</output>

<gadget id="calculator">76 * 12</gadget>
<output>912</output>

<gadget id="calculator">1_200 - 912</gadget>
<output>288</output>

<gadget id="calculator">20 - 12</gadget>
<output>8</output>

<gadget id="calculator">288 / 8</gadget>
<output>36</output>

<gadget id="calculator">36 * 20</gadget>
<output>720</output>

<gadget id="calculator">1_200 - 720</gadget>
<output>480</output>

<gadget id="calculator">64 - 4</gadget>
<output>60</output>

<gadget id="calculator">480 / 60</gadget>
<output>8</output>

<result>8</result>