First, we must calculate the area of the walls Amanda wants to paint. Two of the walls are $5229_w57_h13.png$ and two of the walls are $7064_w57_h14.png$:
So the total square footage of the walls is 500.
If a half gallon of paint will cover 55 square feet, then each gallon will cover 110 square feet. Four gallons would only cover 440 square feet. Five gallons will cover 550 square feet, which will be enough for all 500 square feet of walls.