a)
Total area to be painted=area (wall) - area (door)- area (window)
1) we calculate de area of the wall
area of the wall=area (rectangle)=12 ft x 15 ft=180 ft²
2) we calculate the area of the door:
area of the door=area (rectangle)=8 ft x 3 ft=24 ft²
3) we calculate the area of the window:
area of the window=area (rectangle)=4 ft x 3 ft=12 ft²
4) we calculate the total area to be painted:
area of the wall=180 ft² - 24 ft² - 12 ft²=144 ft²
Answer; the total area to be painted is 144 ft²
b)
we have to find out the number of quarts that we need by the rule of three:
1 quart ---------------------90 ft²
x-----------------------------144 ft²
x=(1 quart x 144 ft²) / 90 ft²=1.6 quarts.
2) now, we find out the total cost by the rule of three:
1 quart----------------------$8
1.6 quarts------------------- x
x=(1.6 quarts x $8) / 1 quart=$12.8
Answer: $12.8.
