$.$ Return to the problem of Exercise $1$ and assume that d $=10,$ p $=3\mathrm{.}5,$ and b $=14.$ Determine $($if necessary, by trying all the possibilities$)$ whether each of the following is a feasible and$/$or optimal solution.

$($a$)$ s $=4$

$($b$)$ s $=6$

$($c$)$ s $=2$