Specific Heat = 2.5 J/g•°C
We can set up an equation to solve this.
(Energy) = (mass)•(specific heat)•(change in temperature)
Plug in what you know
-1500J = 120g•(c)•(40°C-45°C)
[The energy is negative because the energy is lost, and the change in temperature can be found by subtracting the initial temperature from the final temperature (T(Final) - T(Initial))]
Solve
-1500J = 120g•(c)•(40°C-45°C)
-1500J = 120g•(c)•(-5°C)
-1500J = (-600g•°C)•(c)
(-1500J) / (-600g•°C) = c
c = 2.5 J/g•°C