Three processes compose a thermodynamic cycle shown in the accompanying `P-V`, diagram of an ideal gas.
Process `1 rarr 2` take place at constant temperature, during this process `60 J` of heat enters the system.
Process `2 rarr 3` takes place at constant volume. During this process `40 J` of heat leaves the system.
Process `3 rarr 1` is adiabatic.
What is the change in internal energy of the during process `3 rarr 1`?