Chapter 18 - Temperature, Heat, and the First Law of Thermodynamics - Problems - Page 545: 69b

$80$ $J$

The work done across path abc is $80$ $J$ by the first law of thermodynamics and the facts that the inernal energy across the path is 160 J and the heat transferred across the path is 240 J. Since process bc is isochoric, no work is done, so all the work across abc is done in ab. Therefore, $80$ $J$ of work are done along path ab.