Explanation:

- Let the distance be D km and correct time taken be T minutes.

- At 60 km/h, time taken = (D/60) hours = (T + 15) minutes

- At 80 km/h, time taken = (D/80) hours = (T + 7) minutes

- Convert minutes to hours for easier calculation:

• (T + 15)/60 = time at 60 km/h

• (T + 7)/60 = time at 80 km/h

- Equate distances:

• 60 × (T + 15)/60 = 80 × (T + 7)/60

• (T + 15) = 4/3(T + 7)

• 3(T + 15) = 4(T + 7)

• 3T + 45 = 4T + 28

• 4T - 3T = 45 - 28

• T = 17

- So, the correct time is 17 minutes.

- Options explained:

• 17 minutes – Correct

• 18 minutes – No, slightly too high

• 20 minutes – No, result is lower

• 21 minutes – No, significantly higher