Two tall buildings are `30 m` apart. The speed with which a ball must be thrown horizontally from a window `150 m` above the ground in one building so that it enters a window `27.5 m` from the ground in the other building is.
A. `2 m s^-1`
B. `6 m s^-1`
C. `4 m s^-1`
D. `8 m s^-1`