Christopher is going to install wallpaper on the four walls of his room. Two of the walls are 14 feet long by 9 feet high. The other two walls are 20 feet long by 9 feet high. His options at the wallpaper store are below.
One single roll of wallpaper costs $20 and covers 18 square feet of area.
One double roll of wallpaper costs $40 and covers 54 square feet of area.
What is the minimum cost of installing the wallpaper on the four walls of Christopher's room?