HELLO, going through some microeconomics topics and have some questions I need tutoring help with please! :)

Can the perfectly competitive firm affect the market price? Why or why not?

Why does marginal revenue not change when the perfectly competitive firm sells more output?

What happens to economic profits when the firm produces where marginal costs equal the marginal revenue?

When should the perfectly competitive firm shut down?

Are firms permitted to enter or leave an industry in the short run?

What happens in an industry that has economic profits in the long run? (HINT: are firms attracted to this industry?)

Where do the MC, MR, and ATC curves meet in the long run in perfectly competitive markets?

THANK YOU!!