First law of thermodynamics physics basic

Question

Can someone help me with any of these?

U=Q-W

Note: if thermal energy is lost by the system or if work is done to the system, Q or W is negative.

1. 50J of thermal energy is added to a system, 100J of work are done by the system, what is the change of internal energy of the system?
2. 100J of thermal energy is added to a system, 50J of work are done by the system, what is the change of internal energy of the system?
3. 50J of thermal energy are lost by a system, 50J of work are done to the system, what is the change of internal energy of the system?
4. 100J of thermal energy is added to a system, 200J of work are done to the system, Later on 50J of thermal energy are added to the system and 50J of work are done by the system. what is the change of internal energy of the system?

Answer 1

1. ΔU = 50j - 100j = -50j
2. ΔU = 100j - 50j = +50j
3. ΔU = -50j + 50j = 0j
4. ΔU = 100j + 200j + 50j - 50j = +300j