Representation of data — practice question

One end of a light elastic string with natural length $0.7\,\text{m}$ is fixed at point $A$ on a smooth horizontal surface. The other end is fastened to a particle $P$ of mass $0.3\,\text{kg}$, which is initially held at point $B$ on the horizontal surface, where $AB = 1.2\,\text{m}$. It is given that $P$ is released from rest at $B$ and that when $AP = 0.9\,\text{m}$, the particle has speed $4\,\text{m s}^{-1}$.