If 1 additional song costs $0.59, then there would be 26 additional songs downloaded. Because $15.34 divided by $0.59 is 26.
Let x be the number of songs downloaded.
x = 28 + (15.34/0.59)
x = 28 + (26)
x = 54
You have 54 songs downloaded on your tablet.
Hope this helps :)