You're going to need the formula for thermal energy:
\(Q=mc\Delta T\)
Where Q is thermal energy, m is mass, c is the specific heat capacity, and delta T is change in temperature.
SImply plug the variables you were given in question as shown (make sure they're all in the correct units!):
\(84=5\times4.18\times\Delta T\)
\(\Delta T=+4.02°C\)
Add this on to your original temperature, and you get 29°C.