Heat transfer during the process is equal to

Question

Gas contained in a closed system consisting of piston cylinder arrangement is expanded. Work done by the gas during expansion is 50 kJ. Decrease in internal energy of the gas during expansion is 30 kJ. Heat transfer during the process is equal to                      

a. – 20 kJ                     b. + 20 kJ

c. – 80 kJ                     d. + 80 kJ