Consider a router that interconnects four subnets: S$1,$ S$2,$ S$3,$ and S$4.$ Suppose all of

the interfaces in each of these four subnets are required to have the prefix

$199\mathrm{.}100\mathrm{.}8\mathrm{.}0/21.$ You want to divide this address block into four equal$-$sized contiguous

address blocks, and give one of these address blocks to each subnet connected to the

router. Provide network addresses $($of the form a$.$b$.$c$.$d$/$x$)$ that satisfy this

requirement.