In a closed (fixed-mass) system, an ideal gas undergoes a process from an initial state with pressure 517 kPa and volume of 0.1416m³ to a final state with pressure 172.3 kPa and volume of 0.2741m³. For this process, the enthalpy change ΔH is –65.4 kJ and the average constant-volume specific heat c_v,avg is 3.157 kJ/kg·K. Determine:

(a) The internal energy change ΔU.

(b) The average constant-pressure specific heat c_v,avg.

(c) The specific gas constant R.