Let x g be the mass of element in 51.0 g of saturated solution.
Mass of benzene in 51.0 g of saturated solution = 51.0 – x g
Total mass of benzene containing x g of solute = 50 + 51 – x = (101 – x) g
ΔTf=1000KfWBMBWA=1000×5.5×x4×25×(101−x)=0.55(given)⇒x=1.0g
Hence, solubility =WB×100WA=1(51−1)×100=2.0g