This is first an isoceles triangle with base 40' and one of the other two equal sides is 10.5 feet. The two equal sides added together (21 feet) needs to be at least a bit greater than the base (40 feet) to form a triangle. Since this condition is not met it is not possible to have the 3-D object you describe.
A triangle is a two dimensional object and has no volume.
A cubic foot is 12" thick 12" wide and 12" deep. .45 cubic feet per 60# bag of concrete
It depends how thin the cubic feet are. If they are 1 foot thick: 21,000 cubic feet. If they are 3 feet thick: 63,000 cubic feet will cover 21,000 square feet.
It depends upon how thick you want the concrete. For example, if you want the concrete to be 6 inches thick, then you will need 200 cubic feet. There are 27 cubic feet per cubic yard; so divide the 200 cubic feet by 27 to get 7.4 cubic yards.
I think you mean 6 inches thick, not 6 feet thick. You would need 200 cubic feet, or 7.4 cubic yards.
803.84 is the volume in cubic ft when using 3.14 as pi.
Apples and oranges. Without knowing how thick the 450 sq. ft. area is or how thick you want it to be you can't convert to cubic yards. A cubic yard has 27 cubic feet. One square foot 3 inches thick would be 1/4 cubic feet. 4 sq. ft. 3 inches thick would be 1 cubic foot. 450 sq. ft. 3 inches thick is 112 1/2 cubic feet or just a bit over 4 cubic yards. 450 sq. ft. 4 inches thick is 150 cubic feet or 5 1/2 cubic yards.
ONE I THINK, SINCE THERE ARE 27 CUBIC FEET IN A CUBIC YARD OF CONCRETE (WHICH MEASURES 3 FEET BY 3 FEET BY 3 FEET).
Assuming you mean a cubic construct that is 24 feet long by 1 feet wide by 2 feet deep, the answer is 48 cubic feet (24x1x2).
81
5.93 cubic yards.
10' X 11' X 3" X (1'/12") = 27.5 cubic feet 27.5 cubic feet X (1 cubic yard / 27 cubic feet) = 1.02 cubic yards