To find the surface area of the room that needs to be painted, including the floor and ceiling, we first need to calculate the area of each of the four walls.
1. The two walls that are 20 ft. long and 9 ft. high:
2(20 ft. x 9 ft.) = 2(180 sq. ft.) = 360 sq. ft.
2. The two walls that are 15 ft. long and 9 ft. high:
2(15 ft. x 9 ft.) = 2(135 sq. ft.) = 270 sq. ft.
3. The floor area:
20 ft. x 15 ft. = 300 sq. ft.
4. The ceiling area:
20 ft. x 15 ft. = 300 sq. ft.
Adding all these areas together gives us the total surface area to be painted:
360 sq. ft. + 270 sq. ft. + 300 sq. ft. + 300 sq. ft. = 1230 sq. ft.
Therefore, Monica will need to paint a total surface area of 1230 square feet.