The water equivalent of a calorimeter is 10 g and it contains 50 g of water at `15^@C`. Some amount of ice, initially `-10^@C` is dropped in it and half of the ice melts till equilibrium is reached. What was the initial amount of ice that was dropped (when specific heat of ice = `0.5 cal g^-1^@C^-1, specific heat of `water = 1.0 cal g^1^@C^-1` and latent heat of melting of ice `=80 cal g^-1`)?

Options

A. 10 g
B. 18 g
C. 20 g
D. 30 g