Cosine is

which applies to a right triangle. I hope that helps you.
Solve for x.
2x + 4= 8
4x - 88 = -352
x = [?]
If 10% of songs represents 6 songs,
then 100% of songs represents (100 * 6) / 10 = 60 songs
The playlist has a total of 60 songs.
Both companies charge the same amount I am assuming you are asking which to go with?<span />