The water equivalent of a calorimeter is 10g and it contains 50g of water at 15oC. Some amount of ice, initially at −10oC 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 =0.5cal gm−1 oC−1 , specific heat of water =1.0cal gm−1oC−1 and latest heat of melting of ice =80 cal gm−1)?