Rhonda is using the total cost of the item ($85.00) multiplied by the discount (10%) to find the total discount: 85 x 0.10 = 8.50. Once Rhonda subtracts the discount ($8.50) from the total: $85 - $8.50 = $76.50. The other way to look at the problem, is that Rhonda is only paying for 90% of the total cost of the items, instead of 100% since she is receiving the 10% discount. So, she would get the same final total by multiplying the cost of the items ($85.00) by 90%, or 0.90.
