Let the grass in the original pasture be X, and the grass will grow Y every day. According to the topic, the equation is:

x+6y=6*27

x+9y=9*23

The answer is x=72 and y= 15.

When there are 2 1 cow, it is assumed that it will be eaten in n days.

Equation 72+ 15n=2 1n,

Solve n= 12

So 12 days 2 1 cow eats grass.