Aceiling 6 feet by 7 feet can be painted for $52. find the cost of painting a ceiling 18 feet by 21 feet, all things being equal except the dimensions

6 feet * 7 feet = 42 feet²

18 feet * 21 feet = 378 feet²

42 feet²  was painted for $52

1 feet²  will be painted for $52/42

378 feet² will then be painted for:  ($52/42) * 378

                                                       = $468

Hence 18 feet by 21 feet will be painted for $468

Hope this helps.