Answer:
The question does not state how the answer is to be entered. I would use 10% because that is most common.
Explanation:
You are using 300 J of energy to get 30 J of light energy. The fact that you can account for the left over energy is not relevant.
Efficiency = Work Out / Work In
Efficiency = 30 J / 300 J = 0.1
If you need this as a %, you can multiply by 100
Efficiency = 0.1 * 100 = 10%
