Why does dr. king compare his letter to a book?

Read the sentence. the great wave was inexpensive to purchase, costing only about the same as a double of noodles. since lots of copies could be printed and still look good, it made loads of money. which best revises this sentence to create a more formal style and tone? *the great wave was as cheap as buying a double of noodles. since lots of copies could be made and still look great, people started making piles of money. *the great wave was inexpensive to purchase, costing about the same as a double of noodles. since mass quantities could be produced and still look exquisite, it became highly profitable to sell. *the great wave cost next to nothing, practically the same as a double of noodles. since mass quantities could be produced and still look awesome, it became highly profitable to sell. *the great wave was inexpensive to purchase, similar to buying a double of noodles. since lots of copies could be made that still looked amazing, those who sold it made tons of money.