A vapour-compression refrigeration unit using steam as the working fluid operates between \(306 \mathrm{~K}\) and \(280 \mathrm{~K}\). The enthalpy of saturated vapour at \(280 \mathrm{~K}\) is \(2514.20 \mathrm{~kJ} / \mathrm{kg}\) and the enthalpy of saturated liquid at \(306 \mathrm{~K}\) is \(137.82 \mathrm{~kJ} / \mathrm{kg}\). Calculate the COP of the cycle.