Step 1: Formula for torque.
Torque \( \tau \) is related to the change in angular momentum \( \Delta L \) and time \( t \) by:
\[
\tau = \frac{\Delta L}{\Delta t}
\]
Substituting the values \( \Delta L = 4 - 1 = 3 \, \text{J·s} \) and \( \Delta t = 4 \, \text{seconds} \):
\[
\tau = \frac{3}{4} \, \text{J}
\]
Step 2: Conclusion.
Thus, the correct answer is (B) \( \frac{3}{4} \, \text{J} \).