Treasury bills are paying a $4\%$ rate of return. A risk$-$averse investor with a risk aversion of $A=6$ should invest entirely in a risky, portfolio with a standard deviation of $24\%$ only if the risky portolio's expected retum is at least

A$.8\mathrm{.}67\%$

B$.9\mathrm{.}84\%$

C$.21\mathrm{.}28\%$

D$.14\mathrm{.}68\%$