A $$36,000$ portfolio is invested in a risk$-$free security and two stocks. The beta of Stock A is $1\mathrm{.}29$ while the beta of Stock B is $\mathrm{.}90.$ One$-$half of the portfolio is invested in the risk free security. How much is invested in Stock A if the beta of the portfolio is $\mathrm{.}61?$ A$.$ $$14,769$ B$.$ $$12,872$ C$.$ $$17,004$ D$.$ $$12,000$ E$.$ $$15,000$