Suppose That Two Types of Indistinguishable Coffee Beans Are Imported

Suppose that two types of indistinguishable coffee beans are imported to the U.S.: those grown in the mountains of South America and those grown in greenhouses in Canada.Mountain grown coffee produces a better tasting coffee,but buyers cannot distinguish the beans by sight or smell.Only the importers know the source of the beans.Buyers value mountain grown beans at $10 a pound and greenhouse grown beans at $3 a pound.Assume that 70% of imported beans are mountain grown,and 30% are greenhouse grown.
For a naïve buyer,the reservation price of a pound of these coffee beans is

A) $9.80
B) $8.70
C) $7.00
D) $7.90