The ratio of time taken by car A , B, C to cover a certain distance is 3 : 5 : 4. If the car A cover 20 km more than car C in one hour. What is the speed of car B ?

For same distance, speed is inversely proportional to time. Time ratio 3:5:4 means speed ratio is (1/3):(1/5):(1/4) = 20:12:15. If speeds are 20k, 12k, 15k respectively for cars A, B, C. The statement 'car A covers 20 km more than car C in one hour' is ambiguous - it could mean their speeds differ by 20 km/hr, or refer to distances covered in different times. If it means speed difference: 20k - 15k = 20 gives k = 4, so B's speed = 12(4) = 48 km/hr. But 48 km/hr is not among options A, B, or C. The wording is insufficient/ambiguous, making 'None of these' (option E) the correct choice.