Answer:
27,132
Explanation:
Since the order of the books isn't important, we'll use combinations.

where nCr is the number of combinations,
n is the population size,
and r is the sample size.
Here, n = 19 and r = 6.
₁₉C₆ = 19! / (6! (19−6)!)
₁₉C₆ = 19! / (6! × 13!)
₁₉C₆ = 27,132