A university is planning to hold an event at a local venue, which will charge a fixed rental fee of $780 for the event plus $21.90 per guest for food. The university has budgeted $1,025 for administrative and marketing expenses. It plans to hire a band, which will cost another $615. Tickets are expected to sell for $45.30 per guest. Ignore taxes. How many tickets must be sold if the university plans to raise $5,515 in net cash flow from this event?