How do you calculate the square feet of the area?

In a rectangular figure, square feet a generated when you multiply the length of an area by its width.

So if a rectangle is 3 feet long by 5 feet wide, the area is 3 x 5 = 15 square feet.

If you are dealing with a triangle, the area is half the length by the height... so a triangle 3 feet wise at the base, and 5 feet high, would be 0.5 x (3 x 5) = 0.5 x 15 = 7.5 square feet.

If you are dealing with circles, the area is derived from the radius. If the radius is 3 feet, the formula is pi x r2 .... in this case pi x 32 or 9 x pi. Taking pi as 3.14 we get an area of 28.27 sq feet.