Ratio of speeds of A and B=3:4. Time difference between A and B=30 minutes. Concept used: As Speed = distance / time, for constant distance, speed is inversely proportional to time. Calculation: Ratio of time taken by A and B will be inverse of ratio of speeds of A and B=4:3. Let the time taken by A and B be 4 x and 3 x minutes. Time difference between A and B is 30 minutes, 4x−3x=30 x=30 minutes. Time taken by A=4x=4×30=120 minutes =120∕60=2 hours. ∴ Time taken by A is 2 hours.