Toms tunes could play for 7.5 hours because 450/60= 7.5
Sabrina's sounds could play for 8.75 hours because 450-100(set up fee)= 350 and 350/40= 8.75
DJ Derek could play for approximately 9.17 hours because
450-175(set up fee)= 275 and then 275/30= 9.16666667 or approximately 9.17.
Hope this helped you out!