UPSC CDS Math Speed, Time and Distance Questions

Radha and Hema are neighbours and study in the same school. Both of them use bicycles to go to the school. Radha’s speed is 8 km /hr whereas Hem a’s speed is 10 km/hr. Hema takes 9 minutes less than Radha to reach the school. How far is the schoolfrom the locality of Radha and Hema ?