Ball X and ball Y travel towards one another at speeds of $5\,\text{m s}^{-1}$ and $15\,\text{m s}^{-1}$ respectively. They undergo a perfectly elastic head-on collision, and ball Y then moves to the right at a speed of $7\,\text{m s}^{-1}$. What is the speed and direction of ball X following the collision?
- A$3\,\text{m s}^{-1}$ to the left
- B$13\,\text{m s}^{-1}$ to the left
- C$3\,\text{m s}^{-1}$ to the right
- D$13\,\text{m s}^{-1}$ to the right