The energy entering this system is equal to the energy leaving the system. Based on the law of conservation of energy, how many units of energy are entering the system?

A. 5 units

B. 10 units

C. 15 units

D. 20 units

I can't really answer this question without knowing how much energy is leaving the system. If you include that in your question I could answer it for you. But, the amount of energy entering the system would be the same as the amount of energy leaving the system.