Farmer Brian has 2 acres of land. Each acre can support 50 sheep but they differ as to the number of cows that can be supported. One acre can support...

Farmer Brian has 2 acres of land. Each acre can support 50 sheep but they differ as to the number of cows that can be supported. One acre can support 30 cows and the other can support only 10 cows. If he initially has all land supporting cows what is the opportunity cost of one sheep?