There are four walls, one roof and one floor.
Mr. Smith will only paint the walls, but in one of them there is a door not to be painted.
The two walls with no doors have dimensions of 6 feet x 5 feet.
Their individual area is 6 * 5 = 30 square feet.
Their combined area is 2 * 30 = 60 square feet.
The back wall and the front wall have dimensions of 12 feet x 6 feet.
Their individual area is 12 * 6 = 72 square feet.
The front wall has a door of dimensions of 3 feet x 5 feet.
The area of the door is 3 * 5 = 15 square feet.
This area must be subtracted from the area of the fron wall.
Area of the front wall = 72 - 15 = 57 square feet.
The total area to be painted in blue is:
60 + 72 + 57 = 189 square feet