A piece of ice (heat capacity `=2100 J kg^(-1) .^(@)C^(-1)` and latent heat `=3.36xx10^(5) J kg^(-1)`) of mass m grams is at `-5 .^(@)C` at atmospheric pressure. It is given 420 J of heat so that the ice starts melting. Finally when the ice . Water mixture is in equilibrium, it is found that 1 gm of ice has melted. Assuming there is no other heat exchange in the process, the value of m in gram is