What is the change in internal energy if 60 J of heat are released from a system and 20 J of work is done on the system?

The change in internal energy (∆U) can be determined using the first law of thermodynamics, which states that ∆U = Q + W. Here, Q is the heat exchanged (negative when heat is released), and W is the work done on the system (positive). Since 60 J of heat are released, Q = -60 J, and since 20 J of work is done on the system, W = +20 J. Therefore, ∆U = -60 J + 20 J = -40 J. Thus, the change in internal energy is -40 J.