Ineed to how do you make the two equations solving for x and y which is song and pictures.

Let x and y be the no. of files of songs and pictures respectively
by 1st condition we get,

650x + 2200y = 18150
65 x+220y = 1815
13x + 44y = 363

by 2nd condition we get,
x+y = 16
now solve for x and y
and u ll get answer

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