Two building A and B are 20m apart. Building A has a window at a height of 50m above the ground and building B has a window at a height of 30.4m above the ground. With what speed must a man throw a ball horizontally from the window of building A so that it enters the window of building B? (use g=9.8m/`s^(2)`)
a) 5m`s^(-1)`

b) 10m`s^(-1)`

c) 15m`s^(-1)`

d) 20m`s^(-1)`