Ice at $-20^{\circ} \mathrm{C}$ is added to 50 g of water at $40^{\circ} \mathrm{C}$. When the temperature of the mixture reaches $0^{\circ} \mathrm{C}$, it is found that 20 g of ice is still unmelted. The amount off ice added to the water was close to (Specific heat of water $=4.2 \mathrm{J} / \mathrm{g} /{ }^{\circ} \mathrm{C}$ Specific heat of Ice $=2.1 \mathrm{~J} / \mathrm{g} /{ }^{\circ} \mathrm{C}$ Heat of fusion of water at $\left.0^{\circ} \mathrm{C}=334 \mathrm{~J} / \mathrm{g}\right)$