The Trillium lCompany specializes in the purchase, renovation, and resale of elder homes. Trillium employs several carpenters and painters to do the work for Omar Malik, the company founder. It is essential for him to have accurate cost estimates so he can determine total renovation costs before he purchases a piece of property. If estimated renovation costs plus the purchase price of a house are higher than the house's estimated resale value, it is not a worthwhile investment. Dmar has been using the home's interior square feet for his exterior paint cost estimations. Recently he decided to include the number of external openingsthe total number of doors and windows in a houseas a cost driver. Their cost is signicant hEcause they require timeconsuming preparatory work and careful brushwork. The rest of the house usually is painted either by rollers or spray gunsJ which are relatively efcient ways to apply paint to a large area. lIZ'l'mLar has kept careful records of these exterior painting costs on his last 12 jobs: