= Solution
The depicted endpoints have $P_2>P_1$ and $T_2>T_1$. For positive thermal expansion coefficient,
$$
W_a-W_b=V_1\alpha(P_2-P_1)(T_2-T_1)>0.
$$
Thus \b[path (b) requires the least work on the solid, path (a) the most, and path (c) lies midway between them]. Heating at the higher <pressure> produces more negative work on the system. The ordering would reverse for a negative expansion coefficient; if the product vanishes, the paths have equal work in this approximation.
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