Problem Statement: Cold water at $15C$ enters a double$-$pipe counterflow heat exchanger at a rate of $1\mathrm{.}25k\frac{g}{s}$ and is heated to $60C$ by hot water that enters at $100C$ at a rate of $4k\frac{g}{s}.$ Determine the heat exchanger's surface area if the overall heat transfer coefficient is $880\frac{W}{m^2*(K)}.$

Properties: $C_{p,c}=4180\frac{J}{kg*K},c_{p,h}=4190\frac{J}{kg*K}$