STEP - BY - STEP EXPLANATION
What to find?
An expression for the total number of books.
Given:
Number of shelves = 5
Number of books in each shelf = k
If Lucy has a bookcase with 5 shelves and each of this
shelf has k books, then the total number of books can be determine by multiplying the numbers of book by the numbers of shelves.
That is;

ANSWER
5K
38.4 is the answer super easy and could just look it up
Probability? I'm guessing it is asking for a written response so I'll try my best.
If the coin landed heads up 16 times then the probability would be 16/40 which can be reduced to 2/5
If the coin landed tails up 24 times you would do the same so 24/40 and then you can reduce that to 3/5
Part a: The experimental probability of it being tails would be 3/5
Part b: The experimental probability of it being heads would be 2/5
hopefully, I understood the question correctly but I believe this is the right answer