The herdsmen Lao Zhang's family and Lao Wang's family each have a pasture. The area of Lao Wang's pasture is twice the area of Lao Zhang's pasture. Now they want to raise a herd of wild horses on the pasture. If it is stocked on Lao Wang's pasture, it can be stocked on Lao Zhang's pasture for 9 months. And if these wild horses are put together on the pastures of the two families, they will be raised together. At this time, the grass on the pasture will never decrease, so how many months this group of wild horses can graze on the old Wang's pasture will eat up the pasture. (Assume that the thickness of the grass on the two pastures is the same in the first place, and the speed of the grass growth is also the same)
牧民老张家和老王家各有一块牧场，老王家牧场的面积是老张家牧场面积的2倍，现在要在牧场上放养1群野马．如果在老王家的牧场上放养能在老张家的牧场上多放养9个月．而若要是把这群野马放在两家的牧场上一起放养．则此时牧场上的草恰好永远不会减少，那么这群野马能在老王家的牧场上放养多少个月就会将牧草吃光．(假设最初两家牧场上草的厚度一样，草长的速度也一样)
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 2</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">9 / (3/4)</gadget>
<output>12</output>

<result>12</result>