Great American Oilchange (GAO) sells a combined oil change service and parts package for $42. A customer who supplies the parts (oil and filter) is charged $32 for only the service, whereas a customer who buys only the oil and filter (for do-it-yourself use) is charged $32 for the parts. The parts cost GAO $26. equired: 1. Determine the dollar amount of revenue from the oil change service versus the sale of parts for each combined oil change package TIP: To calculate the percentage of the combined package that relates to the service, divide the stand-alone selling price of the service by the combined stand-alone selling prices of both the service and parts. ion Price Parts 9 10 ot 15