<span>The area of a blade with rectangular shape = 1/2 * b * h where b is the base and h, the height.
Here b = 7 and height = 4
So the area of the blade = 1/2 * 7 * 4 = 14ft^2
If the are four blades the total area is the summation of individual blade.
So area = 14 + 14 + 14 + 14 = 56ft^2. Hence none of the option satisfies the answer.</span>