A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is : 

Speed of car in first 15 minutes = 40 km/h

Distance covered = speed $\times$ Time taken

60 minutes = 1 hour

15 minutes = $\frac{15}{60}$ hour

Distance covered = $240\times \frac{15}{60}=10km$

Speed of car in next 15 minutes = 60 km/h

Distance covered = $60\times \frac{15}{60}=15km$

$\therefore$ Total distance covered = (10+15)km = 25 km

$\therefore$ 25 km is correct