In a large study trying to estimate the average risk aversion for a segment of its Aclients, an investment firm finds that the average investor in this segment holds about $75\%$ of his$/$her complete portfolio in a risky portfolio with expected return of $11\mathrm{.}50\%$ and standard deviation of $28\mathrm{.}8\%.$ What is the estimated risk aversion of these clients if the average applicable risk$-$free rate is $3\mathrm{.}2\%?$

$1\mathrm{.}3$

$2\mathrm{.}4$

$0\mathrm{.}4$

$0\mathrm{.}8$