160g= محلول $60{}^\circ C:\frac{60g}{100\,g\,{{H}_{2}}O}\to $ 140g= محلول ${{28}^{{}^\circ }}C:\frac{40g}{100g{{H}_{2}}O}\to $ رسوب$160g\underrightarrow{\,\,\,\,\,\,\,60\to 28\,\,\,\,\,\,\,\,\,}20g$ $X\Rightarrow X=\frac{20\times 20}{160}=2/5$    محلول 20g