You have two cups, one with m1 = 2.73 kg of water at t1 = 42.32oC and the other with m2 = 1.88 kg at t2 = 21.34oC. You mix the two in an insulated thermos. What is the final temperature of the water? I'm pretty sure that this is supposed to be an adiabatic process, because you are trying to keep all of the temperature from going into the outside environment. However, i have absolutely no idea as to how to go about doing this problem.