Explanation:

- To calculate average speed, divide the total distance by the total time.

- Let the one-way distance between village A and B be "D" kilometers.

- Time taken on car from A to B = \( \frac{D}{28} \) hours.

- Time taken on foot from B to A = \( \frac{D}{4} \) hours.

- Total distance covered = \( 2D \) kilometers.

- Total time taken = \( \frac{D}{28} + \frac{D}{4} \) hours.

- Simplify the total time:

$$

\frac{D}{28} + \frac{D}{4} = \frac{D}{28} + \frac{7D}{28} = \frac{8D}{28} = \frac{2D}{7}

$$

- Average speed = \( \frac{2D}{\frac{2D}{7}} = 7 \) km/hr.

- The correct answer is Option 2: 7 km/hr.