Suppose there were x units of grass before, and y units of grass grew every day.

x+6y=6*27

x+9Y=9*23

3Y=45

Y= 15

x=72

Z = x/(21-y) = 72/(21-kloc-0/5) =12 days.

Never finish eating, that is, the amount of grass is exactly equal to the amount of cattle, that is, 15 heads.