Answer:
2 3/8 in.
Step-by-step explanation:

1) Point A will be at (-4,4)
2) I think an equilateral triangle can't be right triangle
Yes you do.
The shelf is 24 in. long, so to fit, the total width of all the cases must be < 24 in.
If each case is 3/8 inches:
60 * 3/8 = 22.5
22.5 < 24, therefore they will all fit.
Lets x = the number of songs
The product of the number of songs and $0.99 = 0.99 times x = 0.99x
The product of the number of songs and $0.99 is $7.92:
=
0.99x = 7.92
Hope that helps.
Your answer would be 4.23 as the answer will be a long one, estimated.