Final answer:
The discount on the sofa is calculated by subtracting the sale price from the original price, resulting in a discount of $137.70.
Step-by-step explanation:
The student is asking about how to calculate the amount of discount that has been applied to the original price of an item to arrive at its sale price. This can be done by subtracting the sale price from the original price. In this case, the sofa's original price was $810 and the sale price is $672.30. To find the discount, we subtract the sale price from the original price:
Original Price - Sale Price = Discount
$810 - $672.30 = $137.70
Therefore, the discount on the sofa is $137.70.