In a counter flow heat exchanger, oil $)=(3\frac{kJ}{k}g-K$ at the rate of $1400k\frac{g}{h}r$ is cooled from $100C$ to $30C$ by water. that enters the exchanger at $20C$ at the rate of $1300k\frac{g}{h}r.$ Determine the heat exchanger area for an overall heat transfer coefficient of $3975k\frac{J}{m^2}hr-K.$ Also derive a relationship between oil and water temperatures at any section of the heat exchanger.

$15$