"Good afternoon, ladies and gentlemen." :)

If it is a formal speech, then use "Good afternoon, ladies and gentlemen." This is not only poilte, but it shows respect also. "Hi or hello everyone" you would use in a less formal, casual situation. :-)

good afternoon

Hi. Is it correct to say- "A pleasant afternoon ma'am *teacher's name* everyone. " "Let me introduce to you our topic for this report" Need help. Ty

Start with ladies and gentlemen