4. (6 points) Sam saved $5,000 from his income last year and decided to deposit it at a bank in a saving account. At the end of the year, his deposit account balance reached a total value of $5,200. During the year, the consumer price index rose from 250 to 265. a. Calculate Sam's nominal interest rate. Show your work. b. Calculate Sam's real interest rate, Show your work. Explain whether Sam experienced an increase or decrease in the purchasing power of his saving over the year. c. Suppose in the following year, the CPI rises to a value of 275. Calculate the nominal interest rate that would allow Sam to maintain the purchasing power of his deposit over this second year. Show your work