A calorimeter of water equivalent 20 g contains 180 g of water at $25^{\circ} \mathrm{C}$. ' m ' grams of steam at $100^{\circ} \mathrm{C}$ is mixed in it till the temperature of the mixture is $31^{\circ} \mathrm{C}$. The value of ' m ' is close to (Latent heat of water $=540$ cal g-1, specific heat of water $=1 \mathrm{cal} \mathrm{g-1}{ }^{\circ} \mathrm{C}^{-1}$ )