1. Jenny found that her cow and got would eat all the grass in a certain field in 45 days, that her cow and goose would eat it in 60 days, but that it would take her goat and goose 90 days to eat it all. If she turns the cow, the goat, and the goose into the field together, how long will it take them to eat all the grass? Assume that the grass is not growing each day.