Assuming the current going rate of US Treasury notes is $2\mathrm{.}5\%,$ what is the cost of debt for Firm Q$?$ Assume Firm Q has a credit risk spread of $4\%$ and a tax rate of $25\%.$

a$.1\mathrm{.}0\%$

b$.2\mathrm{.}5\%$

c$.6\mathrm{.}5\%$

d$.4\mathrm{.}875\%$