Discrete random variables — practice question

A light elastic string has natural length $2\,\text{m}$ and modulus of elasticity $\lambda\,\text{N}$. Its ends are fastened to fixed points $A$ and $B$, which lie at the same horizontal level and are $2.4\,\text{m}$ apart. A particle $P$ of mass $0.6\,\text{kg}$ is attached to the midpoint of the string and hangs in equilibrium at a point $0.5\,\text{m}$ below $AB$ (see diagram).