Solution: 19 ÷ 3 = 6... 1 so it should be 6+ 1=7 people.

Analysis: × ○○○○○○○○

Look at the diagram above.

X is a person and χ is a vacancy.

Because no matter where you sit, you will be adjacent to another audience.

So there is: "×××"

According to one person for every three seats, 19 ÷ 3 = 6... 1 is 7 seats.

I hope it helps you. You can ask me again if you don't understand.