Suppose that the index model for stocks A and $B$ is estimated from excess returns with the following results:

$R_A=2\mathrm{.}8\%+1\mathrm{.}0R_M+e_A$

$R_B=-1\mathrm{.}0\%+1\mathrm{.}3R_M+e_B$

${}_M=($