The company has a certain amount of debt. $($let$$ say $$1000)$

rs $=13\mathrm{.}4\%,$ ro $=12\%.$Calculate the cost of debt.

$->$ some say the answer is COST of DEB $=$ expense $/$ total debt, thus $->$ $$1000*13\mathrm{.}4\%/1000=13\mathrm{.}4\%$

$->$ i have a question that don't i have to use the Ro somehow? please help...