27*6= grassland grass+Zhou Xinsheng 6 grass.

23*9= grassland grass+Zhou Xinsheng 9 grass.

23*9-27*6=45 is the grass of Zhou Xinsheng.

45/3= 15 is 1 week.

So the new grass is enough for 15 cows every week.

Grassland grass 27*6- 15*6=72.

2 1- 15=6 These six cows eat the original grass 72/6= 12 grassland original grass is enough for six cows to eat 12 weeks. So 2 1 cow will be finished in 12 weeks.