A firework initially at rest bursts into four fragments, each moving in a different direction within a horizontal plane. The diagram gives the velocity and mass of each fragment. What is the speed $v$ of fragment X?
- A$200\,\text{m s}^{-1}$
- B$240\,\text{m s}^{-1}$
- C$300\,\text{m s}^{-1}$
- D$360\,\text{m s}^{-1}$