The figure shows the paths of five balls, all thrown at $20\ \text{m/s}$ from the same point, at $15^\circ$, $30^\circ$, $45^\circ$, $60^\circ$ and $75^\circ$. The ball thrown at $30^\circ$ lands at the same spot as one other ball. Which one, and why?

Fig. 1: A graph of height against horizontal distance with the paths of five balls thrown at 20 m/s, at 15, 30, 45, 60 and 75 degrees.