Solutions Part 1

Effective molality =0.6+1.6+0.4=2.6m
As elevation in boiling point is a colligative property which depends on the amount of solute. So, to have same boiling point, the molality of two solutions should be same.
Molality of non-electrolyte solution = molality of K4[Fe(CN)6]=2.6m
Now, 18.1 weight per cent solution means 18.1g solute is present in 100g solution and hence, (100−18.1=)81.9g water.
Now, 2.6=‌

18.1/M

81.9/1000

where, M is the molar mass of non-electrolyte solute
Molar mass of solute, M=85