$16-27$ Use the Spencer slope stability curves to check che factor of safety for a planned embankment where the $\frac{c}{}H$ value is $0\mathrm{.}05,$ is $20,$ and the desired slope inclination is $1\mathrm{.}5$ horizontal to $1$ vertical, if

$($a$)r_u=0$

$($b$)r_u=0\mathrm{.}25$