Let volume of solution is x ml
So mass of solution = 1.2x
& mass of water (solvent) = x gram
So mass of solute = 0.2x gram
Molality = \(\frac{W_{solute} \times 1000}{GMM_{solute} \times W_{solvent}}\)
\(= \frac{0.2x \times 1000}{40\times x}\)
\(= \frac{200}{40}\)
\(= 5\, m\)