2 mole of an ideal gas at 27℃ expands isothermally and reversibly from a volume of 4 litre to 40 litre. the work done (in kJ) by the gas is

a. w = -28.72 kJ
b. w = -11.488 kJ
c. w = -5.736 kJ
d. w = -4.988 kJ