The selling price is $21 and this can be determined by using the unitary method and using the given data.
Given :
A store owner paid $15 for a book she marked up the price of the book by 40%.
The following steps can be used in order to determine the selling price:
Step 1 - The unitary method can be used in order to determine the selling price.
Step 2 - If 100% is $15 then the value of the 40% is given by:
[tex]=\dfrac{40}{100}\times15[/tex]
Step 3 - Simplify the above expression.
= $6
Step 4 - So, the selling price is given by:
= $15 + $6
= $21
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https://brainly.com/question/12116123
