Here are the problems. Can someone please guide me through the steps of solving them? I don't necessarily need the answer although it would be nice! :p

A chemistry student must mix a beaker of hot water with a beaker of cold water in order to obtain a temperature of 37.0°C (body temperature). The temperature of the cold tap water is 22.0°C, and the temperature of the hot tap water is 65.3°C. If a student starts with 60.8 g of cold water, what mass of hot water must be added to reach 37.0°C?

In a coffee-cup calorimeter, 1.82 g of NH4NO3 is mixed with 73.7 g of water at an initial temperature of 25.00°C. After dissolution of the salt, the final temperature of the calorimeter contents is 23.21°C. Assuming the solution has a heat capacity of 4.18 J/°C·g and assuming no heat loss to the calorimeter, calculate the enthalpy change for the dissolution of NH4NO3 in units of kJ/mol.