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

$R_A=3\mathrm{.}6\%+1\mathrm{.}20R_M+e_A$

$R_B=-1\mathrm{.}6\%+1\mathrm{.}50R_M+e_B$

${}_M=($