24×6= 144 unit

2 1×8= 168 units

Grass growing every day: (168-144) ÷ (8-6) =12 unit.

Originally there were grasses: 144- 12×6=72 sets.

If you graze 16 cows, 18 days will be enough. 72 ÷ (16-12) =18 days.

In order to make the pasture never be eaten up, the maximum grazing capacity is 12 cattle.