In an isobaric process (constant presure), the work done by a gas is given by
[tex]W=p \Delta V = p (V_f - V_i)[/tex]
where
p is the gas pressure
[tex]V_f[/tex] is the final volume of the gas
[tex]V_i[/tex] is the initial volume of the gas
In this problem:
[tex]p=200 kPa = 2\cdot 10^5 Pa[/tex]
[tex]V_f=0.120 m^3[/tex]
[tex]V_i=0.200 m^3[/tex]
Therefore, the work done by the gas is
[tex]W=(2 \cdot 10^5 Pa)(0.120 m^3-0.200 m^3)=-1.6 \cdot 10^4 J[/tex]
and the negative sign means the work is done by the environment on the gas.
