Probability — practice question

One end of a light elastic string with natural length $1.6\,\text{m}$ and modulus of elasticity $28\,\text{N}$ is fastened to a fixed point $O$. Its other end is connected to a particle $P$ of mass $0.35\,\text{kg}$, which is hanging at rest vertically beneath $O$. The particle $P$ is launched vertically upwards from the equilibrium position with speed $1.8\,\text{m s}^{-1}$.