Answer:
Option E: 24.
Step-by-step explanation:
When Caleb (C) has 20 more books than Danica (D), we have:
(1)
Now, when Caleb gives Danica half of his books:
(2)
Danica will have 4 more books than Caleb, so:
(3)
Also we have that:
(4)
By entering equation (2) and equation (3) into equation (4) we have:
(5)
From (1) we have:
(6)
By entering (6) into (5):
And, from (6):
Therefore, the correct option is E, Caleb had to start with 24 books.
I hope it helps you!