A farmer has a field where he has cut the grass to a uniform height of 6 cm. The grass there grows uniformly at a constant rate. The farmer has a cow, a horse and a sheep. The
existing grass growing on the ground is enough to feed the three animals together for
20 days. If only the cow and the horse are there, the grass is enough for 25 days; the cow and the sheep
alone, for 33 1/3
days; and the horse and the sheep alone, for 50 days. For how many days could it be sustained
each animal if it were alone in the lot?