Flosstradamus, a popular DJ, is coming to town to perform a concert. Tickets come in three tiers: general admission 1, general admission 2, and VIP.
Flosstradamus sells $400$, $450$, and $100$ tickets for each tier, respectively. Each general admission 1 ticket sells for $\$15$ and the prices of the other tickets are unknown but both are known to be whole numbers less than $\$40$.
What is the maximum amount that VIP tickets can sell for if Flosstradamus brings in $\$9000$ of revenue?