Plaque builds up on the walls of an artery decreasing its diameter from $1\mathrm{.}16$ cm to $0\mathrm{.}68$ cm$.$ If the flow speed is $12\mathrm{.}0$ cm$/$s before reaching the region of plaque buildup, determine the following.

$($a$)$ speed at which blood is traveling through the plaque$-$constricted region