Company ABC has $4-$year zero$-$coupon bonds outstanding, which will pay $$1,000$ at maturity. The assets are valued at $$900,\backslash$sigma $=0\mathrm{.}25,$ r $=0\mathrm{.}045,$ and the company does not pay a dividend. Using a Merton model, what is the yield on debt $($continuously compounded$)?$