Well lets do the work, she wants 5 songs. So let's Multiply
The first three songs she wants are 2.75 each and she wants three so, 2.75 x 3 = 8.25 MB
The second two songs she wants are 3.8 MB each so 3.8 x 2 = 7.6 MB
So let's add the total of those list of songs, 7.6 + 8.25 = 15.85
So your answer is 15.85 MB is what she needs (: