piece of green grass grows at the same rate every day. Now this piece of green grass can feed 10 cows and 60 sheep for 8 days; or 8 cows and 32 sheep can eat for 20 days. It is known that the amount of grass eaten by a cow is equal to the amount eaten by 4 sheep, so how many days can it feed 80 sheep?
一片青草，每天生长的速度相同，现在这片青草可供10头牛和60只羊一起吃8天；或者8头牛32只羊吃20天．已知一头牛的吃草量等于4只羊的吃草量，那么可供80只羊吃多少天．
<gadget id="calculator">64 * 20</gadget>
<output>1_280</output>

<gadget id="calculator">100 * 8</gadget>
<output>800</output>

<gadget id="calculator">1_280 - 800</gadget>
<output>480</output>

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

<gadget id="calculator">480 / 12</gadget>
<output>40</output>

<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<gadget id="calculator">80 - 40</gadget>
<output>40</output>

<gadget id="calculator">8 / 40</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">60 * (1/5)</gadget>
<output>12</output>

<result>12</result>