The correct answer is:
4:18, which means that 4 out of every 18 covers sold are black.
Step-by-step explanation:
To find the ratio of black cases to total, we must first find the total number of cases sold: 5+6+3+4 = 18.
This makes the ratio of black to total 4:18.
The explanation is that 4 cases out of every 18 will be black.