The concentration of residual chlorine is controlled in a process water reactor by varying the flow of a chlorine$-$aluminum polysulfate mixture. The concentration or flow transmitters are calibrated up to $5$ ppm and $200$ mL$/$s$,$ respectively, with zero being the lower range value in both cases. The mixture flows at $120$ mL$/$s$.$ If the set points of the proportional controllers are, respectively, $2\mathrm{.}5$ ppm and $145$ mL$/$s$,$ determine:

a$.$ Valve failure position, and control action of both controllers.

b$.$ Control strategy used. Justify.

c$.$ Block diagram with the respective units.