Steam at $100^\circ$C is passed into 20 g of water at $10^\circ$C. When water acquires a temperature of $80^\circ$C, the mass of water present will be: [Take specific heat of water = 1 cal $g^{–1}$ ${}^\circ$ $C^{–1}$ and latent heat of steam = 540 cal $g^{–1}$ ]