The following table shows the annual effective interest rates being credited by an investment account, by calendar year of investment. The investment year method is applicable for the first 3 years, after which a portfolio rate is used: Investment Year Rates Calendar Year of Portfolio Rate Portfolio Rate 13 Calendar Year of Investment 1990 1991 1992 in 10% iz 10% 1% 1993 8% 12% 5% 10% 1994 (1 - 1)% 8% 12% 1995 6% (1 - 20% 11% 1993 9% 6% 1996 9% 1994 7% 7% 10% 1997 10% An investment of 100 is made at the beginning of years 1990, 1991, and 1992. The total amount of interest credited by the fund during the year 1993 is equal to 28.40. Calculate 1. | O a. 7.25 b. 8.00 C. 7.00 d. 7.50 Oe. 7.75