The total amount financed after the down-payment is $845.00 - $95.00 = $750.00
The total amount of the six monthly payments is 6 * $128.75 = $773.50
So, the total interest Tracy paid is $773.50 - $750.00 = $23.50
Therefore, the total installment price is $773.50 and the total interest is $23.50