Saturated solution = 350cm\(^3\)
mass of salt Z in saturated solution = 55.5g
Number of moles of salt = \(\frac{55.5}{101}\) = 0.55mole

If 350cm\(^3\) of solution contains 0.55mole

  1000cm\(^3\) will contain \(\frac{1000 \times 0.55}{350}\) = 1.57moldm\(^{-3}\)

Alternatively, you can use the formula for solubility which is:

Solubility = \(\frac{mass of solute}{Molar mass of solute}\times\frac{1000}{Volume of solvent}\)

 = \(\frac{55.5}{101}\times\frac{1000}{350}\)

  = 1.571 moldm\(^{-3}\)