E$($r$\_\{$A$\})=16\%$; E$($r B $)=14\backslash \%.$If; sigma$\_\{$A$\}$ Assume that both portfolios A and B are well diversified $,$ that and the economy has only one factor $,$ and $1\mathrm{.}0$ whereas what must be the risk $-$ free rate $?($ Do not round intermediate calculations $.$ Round your answer to two decimal places $.)$ sigma$\_\{$B$\}=0\mathrm{.}8$