using heat balance, mass times heat capacity times temperature difference, the balance looks like:
3.35 * 1000 g * 4.18 J / g C * (20-T) = 1.62 * 1000 g* 80 * 4.1858 J /g + 1.62 * 1000 g * 4.18/2 J / g C * (10.2 C) + 1.62 * 1000 g * 4.18 J /gC * (T-0)
Final temperature, T is equal to 14.29 C