Answer:
The cost of the paper book= $12
Step-by-step explanation:
Hardcover books costs $21
But paper book cost only a fraction of the hardcover book.
The paper book cost 4/7 of the hardcover book.
The cost of paper book= 4/7* paper book
The cost of paper book = 4/7*$21
The cost of the paper book= 4*3
The cost of the paper book= $12
