The mixture, which has an average heat capacity of $3\mathrm{.}0$ kJ$/$kg$.$K and flows through the inner pipe at a speed of $7300$ kg$/$hour$,$ is wanted to be cooled from $102$ C to $39$ C in a double$-$pipe heat exchanger. Water entering at $16$ C is used for cooling and the mass flow rate of water is $4600$ kg$/$hour$.$ Since it is known that the overall heat transfer coefficient is U: $850$ W$/$msquare$.$K$,$ calculate the heat exchanger area for the heat exchangers given below. a$)$ parallel flow b$)$ counter current $($cp$,$ water: $1$ cal$/$g$.$C$)$