It's about Future Bond Price. I think, similar to Future Stock Price, Future Bond Price are calculated by using risk-free rate. But my professor used the Bond Yield instead. I am pretty sure he's wrong, but need your comment to be certain.
if you post the exact question, would be easy to answer in particular.
the general concept is that risk adj rate (YTM) is used to find the FV (or PV) of the bond as long as the bond is not a t-bill/risk free. Risk-free (RF) rate is used is used to value the risk-free bonds/securities.
if needed more, do sens me PM the specific question. i am not sure how reasonable is it to discuss problem not related the gmat on forum...