Given is the shape of a triangle with base = 7 feet and height = 4 feet.
We know the formula for area of triangle is given as follows :-
So, the area of a blade is 14 squared feet.
There are four blades on wind mill. Then area of all four blades would be 4 times 14.
Hence, total area of all four blades = 4 x 14 = 56 squared feet.