If the historical return over the past $30$ years of the S&P $500$ Index is $8\%$ and the risk$-$free rate $($as measured by the $10-$Year Treasury Note$)$ is $4\%,$ what is the equity cost of capital for Summa Corp? If Summa$$s debt trades at Treasuries plus $1\mathrm{.}25\%$ what is Summa$$s WACC? What two factors are the biggest determinants of equity cost?