This is the problem of cattle eating grass, according to

1. (number of cattle * days of more grazing-number of cattle * days of less grazing)/(days of more grazing-days of less grazing) = the amount of grass growing every day.

2. The number of cows * grazing days-the amount of grass growing every day * grazing days = the original amount of grass in the grassland.

Solution: Daily outflow =(6*4-5*4)/(5-4)=4 (person-day)

Original alcohol consumption: 6*4-4*4=8 (person-day)