Dr. Magic charges a flat fee of $350, all money collected above that amount is kept by the school. So, if a school has 800 students paying $3 each to see Dr. Magic's show, the school collects $2,400. After paying Dr. Magic, the school has raised $2,050.
Note: The school sets the admission price for the magic show, not Dr. Magic. So, if a school has, say, 1,000 students and wants to charge $5 for the fundraising show, that's their business. Given that scenario, the school would gross $5,000 and net $4,650 after paying Dr. Magic. Often the admission price is higher for fundraising shows that pure entertainment shows because it's a fundraiser.
Dr. Magic's typical fundraising show runs 45 minutes, but takes up an hour of time. Figure 10 minutes to get everyone into the place where the show will be performed and another 5 minutes to get them out in addition to the show's 45 minutes.