In $1989,$ the CPI was $124\mathrm{.}0.$ In $1990,$ it was $130\mathrm{.}7.$ What was the rate of inflation over this period?

a$.5\mathrm{.}1$ percent

b$.5\mathrm{.}4$ percent

c$.6\mathrm{.}7$ percent

d$.30\mathrm{.}7$ percent

e$.$ You can't tell without knowing the base year.