Answer
$\Delta u = 1.0\ W/kg$
Work Step by Step
For a closed system without changes in potential or kinetic energies:
$Q-W=\Delta U$
If $Q = 1\ W$ and $W = -1.5\ W$
$\Delta U = 2.5\ W$
$\Delta u = \frac{\Delta U}{m} = 1.0\ W/kg$
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