In an isolated system, two objects X and Y undergo a perfectly elastic collision. Their velocities before and after the collision are shown. What is the speed $v$ of Y following the collision?
- A$2.0\ \text{m s}^{-1}$
- B$18\ \text{m s}^{-1}$
- C$22\ \text{m s}^{-1}$
- D$24\ \text{m s}^{-1}$