"1 serving"

The total amount of grass eaten in 20 days is 16×20=320.

The total amount of grass eaten in 12 days is 80÷4× 12=240.

The growth rate of grass is

(320-240)÷(20 days-12 days) = 10 copies/day.

The newly grown grass can feed 10 cows every day.

Grass quantity: 320- 10×20= 120.

10+60÷4=25 N。

10 cows and 60 sheep are equivalent to 25 cows. Eating grass can be arranged as follows:

Among them, 10 cows eat new grass every day.

The remaining 25- 10= 15 cows eat the original grass.

Can eat 120÷(25- 10)=8 days.

10 cattle 60 sheep can eat for 8 days.

(Supplementary note: After 8 days, all the grass growing on the grassland has been eaten up. 15 cows have nothing to eat, but they can be released. 10 cows can continue to eat the new grass growing every day. )