Shantel donates 15% of the 40 books to the national library.
40(.15) = 6
She also sells 3/5 of the 40 books or 60% of it.
3/5 = x/40
Cross multiply
3(40) = 5x
120 = 5x
Divide both sides by 5
x = 24
24 + 6 = 30
Subtract the number of books she sold or donated
40 - 30 = 10
Shantel has 10 books left in her book collection.