Question

A system uses 2,380 J of energy to do work as 12,900 J of heat are added to the system.

Answer 1

The change in internal energy of the system is 10520 J

 From the first law of thermodynamics, the change in internal energy is equal to work done by the system subtracted from the heat added to the system.

i.e.ΔU = Q - W 
Now, as per question, A system uses 2,380 J of energy to do work as 12,900 J of heat are added to the system.

Thus, ΔU = 12900 - 2380 = 10,520 J