Question 388587
Let x = number of $11.50 discs you bought
let y = number of $7.50 discs you bought


Two equations:

x+y=12 (because there are 12 disks bought in total)
11.50x + 7.50y = 110 (because the total cost is $110)


Use substitution or elimination to solve. I will use substitution.


y = 12-x


11.50x +7.50(12-x) = 110
11.50x + 90 -7.5x = 110
4x = 20
x = 5


So there were five $11.50 disks bought. This means there must have been seven $7.50 disks bought.