If a book originally costs $15 and is offered at a 20% discount, what is the sale price?

To determine the sale price of the book after applying the discount, you first calculate the amount of the discount. The discount rate is 20%, which means you multiply the original price of the book by 20% (or 0.20).

Calculating the discount:

[

\text{Discount} = \text{Original Price} \times \text{Discount Rate} = 15 \times 0.20 = 3

]

Once you find the discount amount, you subtract it from the original price to find the sale price:

[

\text{Sale Price} = \text{Original Price} - \text{Discount} = 15 - 3 = 12

]

Therefore, the sale price of the book after applying a 20% discount is $12. This makes the correct answer consistent with the calculations performed, confirming that option B is indeed the right choice.