Answer
$-60$ $J$
Work Step by Step
Along the entire cycle, the total change in internal energy must be zero, so the change in internal energy from c to a along cda must be $200$ $J$. Since 260 J of heat is used along cda and work is only done along cd (as da is isochoric and so has no work done), $-60$ $J$ of work is done on the gas. The negative sign signifies that the gas did positive work.
