A body of mass `50 kg` is projected vertically upward with velocity of `100 m//s`. After `5 s` this body breaks into `20 kg` and `30 kg`. If the `20 kg` piece travels upwards with `150 m//s`, then the velocity of other block will be
A. 15m/sec downwards
B. 15m/sec upwards
C. 51m/sec downwards
D. 51m/sec upwards