Farmer Mohan owns a piece of grassland and three animals: a cow, a buffalo, and a donkey. Mohan discovered the following:
When the cow and the buffalo graze on the field together, there is no more grass after 45 days.
When the cow and the donkey graze on the field together, there is no more grass after 60 days.
When the cow grazes on the field alone, there is no more grass after 90 days.
When the buffalo and the donkey graze on the field together, there is no more grass after 90 days also
For how long can the three animals graze on the field together?
