Salt solution $($C$\_\{$P$\}=3$kJ $/$ k $*$ gK$)$ at a rate of $300$kg $/$ m $*$ in is heated in a $2-4$ heat exchanger from $25\backslash$deg C to $90\backslash$deg C$.$ Heating medium is oil $($C$\_\{$r$\}=2$kJ $/$ k $*$ gK$)$ and enters the heat exchanger at $140\backslash$deg C$.$ The flow rate of oil is $400$kg $/$ min. Determine required heat transfer area if overall heat transfer coefficient is $400$ W $/($m $^2)*$ K $.$