(1) Solution: Suppose there are 320 people at the ticket office x minutes after the ticket sales start.

400+4x-2×3x=320

x=40

A: 40 minutes after the ticket sales started, there were 320 people at the ticket office.

(2) Solution: Assume that Y ticketing windows are opened at the same time.

20×3y=400+20×4

y=8

A: At the same time, 8 ticket sales windows were opened.