7. A thermodynamic process is shown in the figure. The pressures and volumes corresponding to some points in the figure are :

P_A=3×10⁴ Pa and  P_B=8×10⁴ Pa, V_A=2×10^-3 m³ and V_D=5×10^-3 m³ . In process AB, 600 J of heat is added to the system and in process BC, 200 J of heat is added to the system. The change in internal energy of the system in process AC would be

(a)   560 J

(b)  800 J

(c)   600 J

(d)  640 J

Answer-a