A stock has an expected return of $10\mathrm{.}45$ percent, its beta is $\mathrm{.}85,$ and the expected return on the market is $11\mathrm{.}8$ percent. What must the risk$-$free$$rate be$?$Input area:Stock E$($R$)10\mathrm{.}45\%$ Stock beta $0\mathrm{.}85$ Market E$($R$)11\mathrm{.}80\%($Use cells A$6$ to B$8$ from the given information to complete this question.$)$Output area:Risk$-$free

I need the actual formula for excel for this problem.