2. Let the daily grass consumption of Niu Yi be a unit, then the grass consumption of 15 cows is: 1 ×15× 8 =120 (unit1).

The amount of grass eaten by 22 cows is: 1×22×4=88 (unit 1).

Variance: 120-88=32 (unit 1)

In other words, grass grows in 8-4=4 (days).

Grass growing every day: 32÷4=8 (unit 1)

8 ÷ 1=8 (head) You can put eight cows and never finish them.