On January 1, 2015, Anna invested $5,000 at 5 percent interest for one year. The CPI on January 1, 2015 stood at 2.37. On January 1, 2016, the CPI was 2.40. The real rate of interest earned by Anna was ______ percent.
a) 9
b) –5
c) 3.7
d) 5