The first law of thermodynamics states that:
\[
\Delta U = Q - W
\]
Since the internal energy change \( \Delta U \) is the same for both paths, we can equate the two expressions for \( \Delta U \) and solve for \( W \) along path \( ibf \). This gives \( W = 16 \, \text{cal} \).
Final Answer:
\[
\boxed{16 \, \text{cal}}
\]