Hello! could someone please explain how to solve the question attached, I have trouble working this out by myself. Further, would you be able to explain how a set is closed, bounded or convex? Thanks!

5. A lm's prtuiucrion set is Y = {(1. y} E R5 = y s 15} a. Is this set closed? Explain. b. Is this set bounded? Explain C. Is this set convex? Explain d. Explain why we would interpret a boundary point of the set as "efficient\" and an interior point as "inefficient.\