Markup (or price spread) is the difference between the selling price of a good or service and cost.
Given:
Markup = $8.45
Selling Price = $42.25
Percent Mark up is given as

Since
Markup = Selling Price - Cost Price
This implies
Cost Price = Selling Price - Markup
Hence

Hence, percent Markup is calculated as

Simplify the equation

Therefore, the percent markup is 25%