If the Federal Reserve buys $4 million in bonds from the public and the reserve requirement in the banking system is 20% (assume that banks are fully loaned up), then there will be:

a. a decrease in the money supply of $100 million.
b. an increase in the money supply of $80 million.
c. an increase in the money supply of $20 million.
d. a decrease in the money supply of $25 million.