Probability — practice question

Two light elastic strings have one end fixed to a horizontal beam. One has natural length $0.6\,\text{m}$ and modulus of elasticity $12\,\text{N}$, while the other has natural length $0.7\,\text{m}$ and modulus of elasticity $21\,\text{N}$. Their other ends are joined to a small block $B$ of weight $W\,\text{N}$. The block is suspended in equilibrium $d\,\text{m}$ below the beam, with both strings vertical.