If the nominal rate of return is $12\mathrm{.}64\%$ and the real rate of return is $6\mathrm{.}29\%,$ at what rate are costs changing?

Enter your answer as a percentage with four decimal places but without the percent symbol. For example, if your answer is $90\mathrm{.}1234\%,$ enter

$90\mathrm{.}1234$