How is the sun part of a closed system?

If the sun is the system, then the space around it will be surroundings including the Planet Earth. The sun gives us the light which is made up of photons, which has 0 rest mass, so light is not a matter. So, we can say the only energy gets to transfer and hence it's a closed system.

answer; economic order quantity;

i think it's c. i'm not sure but i think so.