The three processes in a thermodynamic cycle shown in the figure are : Process 1→2 is isothermal; Process 2→3 is isochoric (volume remains constant); Process 3→1 is adiabatic. The total work done by the ideal gas in this cycle is 10J. The internal energy decreases by 20J in the isochoric process. The work done by the gas in the adiabatic process is −20J. The heat added to the system in the isothermal process is