In thermodynamics, work performed by a system is the energy transferred by the system to its surroundings. It is calculated by the integral of pressure and volume of the system. At constant pressure, the expression for work would be as follows:
W = P(V2-V1)
W = 1.21(3.35 -5.64) = -2.77 L-atm
W = -2.77 (101.33) = -280.78 J