From the meaning of the problem, when an ideal gas with a certain mass changes from state A to state B through process I,

W 1 is negative work and Q 1 is positive (endothermic).

△ u = w1+q1=120, and the internal energy can be increased by 120J. ..

When the gas returns from state b to state a through process II,

W2 is active work; △U′= W2+Q2 =- 120j

Q2=-320J, giving off heat.

So the answer is: the heat released by the gas in this process is 320 J.