you can proceed like this,
650 kb for a pic
and 2200kb for song ( 650 + 1550)
total= 18150 kb and 16 files
so, 650 kb each in both pic and song = 16 * 650= 10400
remaining = 18150-10400 = 7750 , which is contributed by additional 1550 of songs that is
7750/1550 = 5
so, a total of 5 songs and 11 pictures were sold..
hope it helped