Answer:
If the store marks up the price of the diving board by 45%, the selling price will be 100% + 45% = 145% of the cost price.
Let's calculate the selling price:
Selling price = Cost price + Mark-up
Mark-up = Selling price - Cost price
Mark-up = (145% of cost price) - cost price
Mark-up = 0.45 * cost price
We know that the store paid $261 for the diving board, so:
Mark-up = 0.45 * $261 = $117.45
Therefore, the amount of the mark-up is $117.45.