The spot rate of exchange, S(MXN/USD), between the Mexican peso (MXN) and U.S. dollar (USD) is MXN 11.95/USD and the 6-month futures rate is MXN 12.4328/USD. If U.S. interest rates are 5% per annum then the annual interest rate in Mexico must be
a. 6.64%
b. 13.28%
c. 17.4%
d. 22.6%