Explanation:

- Calculate the time difference between going at 8 km/h and 12 km/h.

- At 12 km/h, he reaches 7 minutes early. Convert 7 minutes to hours: 7/60 hours.

- At 8 km/h, he reaches 14 minutes late. Convert 14 minutes to hours: 14/60 hours.

- The total time difference is 7/60 + 14/60 = 21/60 = 0.35 hours.

- Let the distance be $d$ km.

- Using the formula $\text{Time}=\frac{\text{Distance}}{\text{Speed}}$:

- Time at 12 km/h is $\frac{d}{12}$.

- Time at 8 km/h is $\frac{d}{8}$.

- The time difference equation: $\frac{d}{8}-\frac{d}{12}=0.35$.

- Solving: $\frac{3d-2d}{24}=0.35\Rightarrow \frac{d}{24}=0.35\Rightarrow d=8.4\text{ km}$.

Correct Answer: Option 3 - 8.4 km

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