A process is carried out at constant volume. It is found that the entropy change is \(1.0 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}\). If \(C_{V}=0.918 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}\) and the lower temperature of the process is \(18^{\circ} \mathrm{C}\), then determine the upper temperature of the process.