When Kai took out his first two year membership with Orange gym in 2010 the fee was $540. He renewed his membership three times: in 2012 for $580, 2014, for $600, and in 2016, for $630. What is the non-annualized, overall rate of inflation for Kai's gym membership?

a. 7.87%

b. 5.4%

c. 16.66%

d. 8.6%