If the current inflation rate is $1\mathrm{.}50\%$ and you have an investment opportunity that pays $8\mathrm{.}40\%,$ then the real rate of interest on your investment is closest to $$

A$.8\mathrm{.}20\%$

B$.10\mathrm{.}90\%$

C$.9\mathrm{.}50\%$

D$.6\mathrm{.}80\%$