To calculate the total area of the walls that need to be painted, we need to calculate the area of each wall separately and subtract the areas of the windows and the door.
1. Area of the first wall:
Height: 9 ft
Width: 12 ft
Area = Height x Width
Area = 9 ft x 12 ft = 108 sq ft
2. Area of the second wall:
Height: 9 ft
Length: 11 ft
Area = Height x Length
Area = 9 ft x 11 ft = 99 sq ft
3. Area of the third wall:
Height: 9 ft
Width: 12 ft
Area = Height x Width
Area = 9 ft x 12 ft = 108 sq ft
Now, let's calculate the area that does not need to be painted:
1. Area of the door:
Height: 7 ft
Width: 3.5 ft
Area = Height x Width
Area = 7 ft x 3.5 ft = 24.5 sq ft
Therefore, the total area of the walls to be painted is:
Total area = (Area of first wall + Area of second wall + Area of third wall) - Area of the door
Total area = (108 sq ft + 99 sq ft + 108 sq ft) - 24.5 sq ft
Total area = 315.5 sq ft
Since 1 gallon of paint covers 102 sq ft, Ingrid should buy:
Total gallons = Total area / 102 sq ft
Total gallons = 315.5 sq ft / 102 sq ft
Total gallons = 3.09
Therefore, Ingrid should buy approximately 3.09 gallons of paint.