The risk$-$free rate is $5\mathrm{.}25\%.$ The expected return on the market is $12\%$ with a standard deviation of $18\%.$ What is the standard deviation of an efficient portfolio with a $16\%$ expected return? $7\mathrm{.}33\%10\mathrm{.}12\%28\mathrm{.}67\%19\mathrm{.}11\%$