3.0 moles of gas expand from an initial volume of 0.040 m 3 to a final volume of 0.085 m 3 while the temperature of the gas is kept fixed at 300 K.

3.0 moles of gas expand from an initial volume of 0.040 m3 to a final volume of 0.085 m3 while the temperature of the gas is kept fixed at 300 K. How much work is done by the system?

I know that the answer is suppose to be 5.6 kJ but I do not know how that answer is derived.