Need to find change of energy during work

a system has 2.50 × 102 kcal of work done to it, and releases 5.00 × 102 kJ of heat into its surroundings, what is the change in internal energy of the system?

You are adding 2.50 x 10^2 kcal and releasing 5.00 x 10^2 kJ. So the difference is the change in internal energy of the system. You will need to convert kcal to kJ or vice verse to do the subtraction